wiki:FCS-Specification-ScrapBook

Version 82 (modified by Oliver Schonefeld, 11 years ago) (diff)

trim old discussion

FCS Specification Scrapbook

Issues with current document

  1. Uncomprehensible and not well structured :(
  2. Resource enumeration (aka scan on fcs.resource) rather complex and unintuitive
  3. Basic KWIC records has no provision for multiple "highlight" hits
  4. No (clear) recommendation for using Resource and ResouceFragment
  5. What about recursiveness in Resource (see current schema)? What is the use case?

General ideas / design goals towards better specification

  1. Define FCS conformance level independent of what SRU/CQL do. Don't call them "level", but maybe something like profile to avoid confusion.
    1. Do a basic profile first
    2. Do an advanced/extend profile later in a separate specification or specification amendment (which must be, of course, compatible to basic profile)
    3. Add provisions to, e.g. explain output, to allow endpoints to indicate the profile, they support
  2. Better structure of document (and don't include aggregation stuff; that's a different specification; implementors of endpoints should not need to worry about aggregator implementation)
  3. Keep XML sanity always in mind (so there are no namespace issues as in CMDI)
  4. Drop resource enumeration in favor of endpoint resource description
  5. Drop the recursiveness of Resource, content models should be: Resource (DataView*, ResourceFragment*) and ResourceFragment (DataView*)
  6. Drop the KWIC data view in favor of HITS data view; the latter will allow for multiple hit highlights
  7. Honor and use extension hooks provided by SRU/CQL
  8. Non-normative stuff
    1. Endpoint specific extension hooks, e.g. to avoid tag abuse of DataView. Resource.xsd could provide an extension hook, so arbitrary XML could also be embedded.
  9. Do we want to keep Images (IMG) and Geolocation (KML) as defined Data View in "basic" profile?

TODOs for the current draft / Preliminary items identified by discussion (in no particular order)

  1. Explicitly list supported Data Views by collection: Amend the Endpoint Description to explicitly encode which Data Views are supported by a given collection. The semantics between parent-child is, that children MUST "inherit" the Data Views of the parent, i.e. a child collection must support all Data Views supported by the parent collection. Something along the lines of: 
    <ed:EndpointDescription xmlns:ed="http://clarin.eu/fcs/endpoint-description">
  <ed:Profile>basic</ed:Profile>
  <ed:SupportedDataViews>
    <ed:SupportedDataView id="dv1">application/x-clarin-fcs-hits+xml</ed:SupportedDataView>
    <ed:SupportedDataView id="dv2">application/x-cmdi+xml</ed:SupportedDataView>
    <ed:SupportedDataView id="dv3">image/png</ed:SupportedDataView>
  </ed:SupportedDataViews>
  <ed:Collections>
    <ed:Collection pid="http://hdl.handle.net/4711/0815">
      <!-- NB: regular stuff skipped -->
      <ed:SupportedDataViews ref="dv1" />
    </ed:Collection>
    <ed:Collection pid="http://hdl.handle.net/4711/0816">
      <!-- NB: regular stuff skipped -->
      <ed:SupportedDataViews ref="dv1 dv2" />
    </ed:Collection>
    <ed:Collection pid="http://hdl.handle.net/1">
      <!-- NB: regular stuff skipped -->
      <ed:SupportedDataViews ref="dv1 dv2 dv3" />
      <ed:Collections>
        <ed:Collection pid="http://hdl.handle.net/1/1">
          <!-- NB: regular stuff skipped -->
          <ed:SupportedDataViews ref="dv1 dv2" />
        </ed:Collection>
        <ed:Collection pid="http://hdl.handle.net/1/2">
          <!-- NB: regular stuff skipped -->
          <ed:SupportedDataViews ref="dv1 dv3" />
        </ed:Collection>
      </ed:Collections>
    </ed:Collection>
  </ed:Collections>
</ed:EndpointDescription>
  2. Endpoint Capabilities: <Capability> elements in the Endpoint Description verbosely describe capabilities of an Endpoint in a more fine grained fashion than a Profile. A Profile is a collection of capabilities. Endpoint Description could look like the following: 
    <ed:EndpointDescription xmlns:ed="http://clarin.eu/fcs/endpoint-description">
  <ed:Profile>basic</ed:Profile>
  <ed:Capabilities>
    <!-- capabilities should be identified by closed vocabulary; maybe encoded by URIs? -->
    <ed:Capability>http://clarin.eu/fcs/1.0/feature/basic-search</ed:Capability>
    <!-- actually the next would already be an extended capability beyond the basic profile -->
    <ed:Capability>http://clarin.eu/fcs/1.0/feature/query-expansion</ed:Capability>
  </ed:Capabilities>
  <!-- other EndpointDescription stuff ... -->
</ed:EndpointDescription>
    This is nor yet very useful for the basic Profile, but will be useful for extended Profile(s).
  3. Need-to-Request Data Views: Data Views will be classified into a "send-by-default" and a "need-to-request" class (which need to be documented in the spec analogous to the payload disposition). The first would indicate, that the Endpoint will include this data view unconditionally, e.g. the Generic Hits view. For the second class, a Client explicitly needs to request the Data View by using another custom query parameter (x-fsc-request-dataviews?) and supplying a (list of) data view(s). The Endpoint Description should also indicate to which class a data views to. This way, Endpoints could also indicate, that they e.g. always include some data view, that has been marked as "need-to-request" by the spec. This change would enable FCS to add/define Data Views that are too "expensive" (e.g. in terms of computational power or bandwidth) to generate for every request.

Proposal for new specification: Federated Content Search - Core Specification

The following is a proposal for a revisited federated content search specification. When done, cut and paste to the appropriate section of the Wiki and publish on the CLARIN web page.

CLARIN Federated Content Search (CLARIN-FCS) - Core

  1. FCS Specification Scrapbook
    1. Issues with current document
    2. General ideas / design goals towards better specification
    3. TODOs for the current draft / Preliminary items identified by …
    4. Proposal for new specification: Federated Content Search - Core …
  2. CLARIN Federated Content Search (CLARIN-FCS) - Core
    1. Introduction
      1. Terminology
      2. Glossary
      3. Normative References
      4. Non-Normative References
      5. Typographic and XML Namespace conventions
    2. CLARIN-FCS Interface Specification
      1. Capabilities and Profiles
      2. Result Format
        1. Resource and ResourceFragment
        2. Data View
          1. Generic Hits (HITS)
      3. Endpoint Description
      4. Endpoint Custom Extensions
    3. CLARIN-FCS to SRU/CQL binding
      1. SRU/CQL
      2. Operation explain
      3. Operation scan
      4. Operation searchRetrieve
    4. Normative Appendix
      1. List of extra request parameters
      2. List of diagnostics
    5. Non-normative Appendix
      1. Referring to an Endpoint from a CMDI record
      2. Endpoint custom extensions
      3. Endpoint highlight hints for repositories
    6. Proposal for new specification: Federated Content Search - Data Views
  3. CLARIN Federated Content Search (CLARIN-FCS) - Data Views
    1. Introduction
      1. Terminology
      2. Normative References
      3. Non-Normative References
      4. Typographic and XML Namespace conventions
    2. Data Views
      1. Generic Hits (HITS)
      2. Component Metadata (CMDI)
      3. Images (IMG)
      4. Geolocation (GEO)
  4. Discussion

Introduction

The goal of the CLARIN Federated Content Search (CLARIN-FCS) - Core specification is to introduce a interface specification, that decouples the search engine functionality from its exploitation, i.e. user-interfaces, third-party applications and to allow services to access heterogeneous search engines in a uniform way.

Terminology

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in RFC2119.

Glossary

Aggregator
A module or service to dispatch queries to repositories and collect results.
CLARIN-FCS, FCS
CLARIN federated content search, an interface specification to allow searching within resource content of repositories.
Client
A software component, that implements the interface specification to query Endpoints, i.e. an aggregator or a user-interface.
CQL
Contextual Query Language, previously known as Common Query Language, is a formal language for representing queries to information retrieval systems such as search engines, bibliographic catalogs and museum collection information.
Endpoint
A software component, that implements the CLARIN-FCS interface specification and translates between CLARIN-FCS and a search engine.
Hit
A piece of data returned by a Search Engine that matches the search criterion.
Interface Specification
Common harmonized interface and suite of protocols that repositories need to implement.
Search Engine
A software component within a repository, that allows for searching within the repository contents.
SRU
Search and Retrieve via URL, is a protocol for Internet search queries.
Data View
A Data View is a mechanism to support different representations of search results, e.g. a "hits with highlights" view, an image or a geolocation.
Data View Payload, Payload
The actual content encoded within a Data View, i.e. a CMDI metadata record or a KML encoded geolocation.
PID
A Persistent identifier is a long-lasting reference to a digital object.
Repository
A software component at a CLARIN center that stores resources (= data) and information about these resources (= metadata).
Repository Registry
A separate service that allows registering Endpoints and provides information about these to other components, e.g. an aggegator. The ​CLARIN Center Registry is an implementation of such a repository registry.

Normative References

RFC2119
Key words for use in RFCs to Indicate Requirement Levels, IETF RFC 2119, March 1997,
​http://www.ietf.org/rfc/rfc2119.txt
XML-Namespaces
Namespaces in XML 1.0 (Third Edition), W3C, 8 December 2009,
​http://www.w3.org/TR/2009/REC-xml-names-20091208/
OASIS-SRU-Overview
searchRetrieve: Part 0. Overview Version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part0-overview/searchRetrieve-v1.0-os-part0-overview.doc ​(HTML), ​(PDF)
OASIS-SRU-APD
searchRetrieve: Part 1. Abstract Protocol Definition Version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part1-apd/searchRetrieve-v1.0-os-part1-apd.doc ​(HTML) ​(PDF)
OASIS-SRU12
searchRetrieve: Part 2. SRU searchRetrieve Operation: APD Binding for SRU 1.2 Version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part2-sru1.2/searchRetrieve-v1.0-os-part2-sru1.2.doc ​(HTML) ​(PDF)
OASIS-CQL
searchRetrieve: Part 5. CQL: The Contextual Query Language version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part5-cql/searchRetrieve-v1.0-os-part5-cql.doc ​(HTML) ​(PDF)
SRU-Explain
searchRetrieve: Part 7. SRU Explain Operation version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part7-explain/searchRetrieve-v1.0-os-part7-explain.doc ​(HTML) ​(PDF)
SRU-Scan
searchRetrieve: Part 6. SRU Scan Operation version 1.0, OASIS, January 2013,
​http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/part6-scan/searchRetrieve-v1.0-os-part6-scan.doc ​(HTML) ​(PDF)
LOC-SRU12
SRU Version 1.2: SRU Search/Retrieve Operation, Library of Congress,
​http://www.loc.gov/standards/sru/sru-1-2.html
LOC-DIAG
SRU Version 1.2: SRU Diagnostics List, Library of Congress,
​http://www.loc.gov/standards/sru/diagnostics/diagnosticsList.html

Non-Normative References

RFC6838
Media Type Specifications and Registration Procedures, IETF RFC 6838, January 2013,
​http://www.ietf.org/rfc/rfc6838.txt
RFC3023
XML Media Types, IETF RFC 3023, January 2001,
​http://www.ietf.org/rfc/rfc3023.txt

Typographic and XML Namespace conventions

The following typographic conventions for XML fragments will be used throughout this specification:

  • <prefix:Element>
    An XML element with the Generic Identifier Element that is bound to an XML namespace denoted by the prefix prefix.
  • @attr
    An XML attribute with the name attr
  • string
    The literal string must be used either as element content or attribute value.

Endpoints and Clients MUST adhere the XML-Namespaces specification. The CLARIN-FCS interface specification generally does not dictate whether XML elements should be serialized in their prefixed or non-prefixed syntax, but Endpoints MUST ensure that the correct XML namespace is used for elements and that XML namespaces are declared correctly. Clients MUST be agnostic to which syntax for serializing the XML elements, i.e. if the prefixed or un-prefixed variant was used, and SHOULD operate solely on expanded names, i.e. pairs of namespace name and local name.

The following XML namespace names and prefixes are used throughout this specification. The column "Recommended Syntax" indicates, which syntax variant SHOULD be used by the Endpoint to serialize the XML response.

Prefix Namespace Name Comment Recommended Syntax
fsc http://clarin.eu/fcs/resource CLARIN-FCS Resources prefixed
ed http://clarin.eu/fcs/endpoint-description CLARIN-FCS Endpoint Description prefixed
hits http://clarin.eu/fcs/dataview/hits CLARIN-FCS Generic Hits prefixed
sru http://www.loc.gov/zing/srw/ SRU prefixed
diag http://www.loc.gov/zing/srw/diagnostic/ SRU Diagnostics prefixed
zr http://explain.z3950.org/dtd/2.0/ SRU/ZeeRex Explain prefixed
cmdi http://www.clarin.eu/cmd/ Component Metadata un-prefixed
kml http://www.opengis.net/kml/2.2 Keyhole Markup Language un-prefixed

CLARIN-FCS Interface Specification

The CLARIN-FCS interface specification defined two profiles, an extensible result format and a set of required operations. CLARIN-FCS is built on the SRU/CQL standard and additional functionality required for CLARIN-FCS is added through SRU/CQL's extension mechanisms.

Generally, CLARIN-FCS Interface Specification consists of two components, a set of formats and a transport protocol. The Endpoint component is a software component that acts as a bridge between the Formats, that are send by a Client using the Transport Protocol, and a Search Engine. The Search Engine is a custom software component, that allows searching in the language resources of a CLARIN center. The Endpoint basically implements the transport protocol and acts as an mediator between the CLARIN-FCS specific formats and the idiosyncrasies of Search Engines. The following figure illustrates the overall architecture. 

                 +---------+
                 |  Client |
                 +---------+
                     /|\
                      |
          -------------------------
         |        SRU / CQL        |
         | w/CLARIN-FCS extensions |
          -------------------------
                      |
                     \|/
 +-----------------------------------------+
 |        |      Endpoint     /|\          |
 |        |                    |           |
 |  ---------------    ------------------  |
 | | Translate CQL |  | Translate Result | |
 |  ---------------    ------------------  |
 |        |                    |           |
 |       \|/                   |           |
 +-----------------------------------------+
                     /|\
                      |
                     \|/
        +---------------------------+
        |       Search Engine       |
        +---------------------------+

In general, the work-flow in CLARIN-FCS is as follows: a Client submits a query to an Endpoint. The Endpoint translates the query from CQL to the dialect used by the Search Engine and submits the translated query to the Search Engine. The Search Engine processes the query and generates a result set, i.e. it compiles a set of hits that match the search criterion. The Endpoint then translates the results from the Search Engine specific result set format to the CLARIN-FCS result format and sends it to the Client.

The following sections describe the CLARIN-FCS profiles and query and result formats, how SRU/CQL is used as a transport protocol in the context of CLARIN-FCS and the required CLARIN-FCS specific extensions to SRU.

Capabilities and Profiles

CLARIN-FCS defines two profiles:

Basic profile
Endpoints MUST support term-only queries.
Endpoints SHOULD support terms combined with boolean operator queries (AND and OR), including sub-queries. Endpoints MAY also support NOT or PROX operator queries. If the Endpoint does not support a query, i.e. the used operators are not supported by the Endpoint, it MUST return an appropriate error message using the appropriate SRU diagnostic.
Examples for valid CQL queries for the basic profile: 
cat
"cat"
cat AND dog
"grumpy cat"
"grumpy cat" AND dog
"grumpy cat" OR "lazy dog"
cat AND (mouse OR "lazy dog")
The Endpoint MUST perform the query on an annotation tier, that makes the most sense for the user, i.e. the textual content for a text corpus resource or the orthographic transcription of a spoken language corpus. Endpoints SHOULD perform the query case-sensitive.
If an Endpoint only supports the basic profile, it MUST NOT silently accept queries that include CQL features besides term-only and terms combined with boolean operator queries, i.e. queries involving context sets, etc.
Extended profile
This profile will support more sophisticated queries such as selecting annotation tiers, expanding of tags, or mapping of data categories.
NOTE: the extended profile is not yet defined and will be part of a future CLARIN-FCS specification.

Endpoints and Clients MUST support the basic profile. For now, Endpoints and Clients MUST NOT claim to support the extended profile.

Result Format

The Search Engine will produce a result set containing several hits as the outcome of processing a query. The Endpoint MUST serialize these hits in the CLARIN-FCS result format. Endpoints are REQUIRED to adhere to the principle, that one hit MUST be serialized as one CLARIN-FCS result record and MUST NOT combine several hits in one CLARIN-FCS result record. E.g., if a query matches five different sentences within one text (= the resource), the Endpoint must serialize five Resource (= one per hit) and embed each within one SRU result (see below).

CLARIN-FCS uses a customized format for returning results. Resource and Resource Fragments serve as containers for hit results, that are presented in one or more Data View. The following section describes the Resource format and Data View format and section Operation ''searchRetrieve'' will describe, how hits are embedded within SRU responses.

Resource and ResourceFragment

To encode search results, CLARIN-FCS supports two building blocks:

Resources
A Resource is an searchable entity at the Endpoint, such as a text corpus or an multi-modal corpus. A resource SHOULD be a self-contained unit, i.e. not a sentence in a text corpus or a time interval in an audio transcription.
Resource Fragments
A Resource Fragment is a smaller unit in a Resource, i.e. a sentence in a text corpus or a time interval in an audio transcription.

A Resource SHOULD be the most precise unit of data that is directly addressable as a "whole". A Resource SHOULD contain a Resource Fragment, if the hit consists of just a part of the Resource unit (for example if the hit is a sentence within a large text). A Resource Fragment SHOULD be addressable within a resource, i.e. it has an offset or a resource-internal identifier. Using Resource Fragments is OPTIONAL, but Endpoints are encouraged to use them. If the Endpoint encodes a hit with a Resource Fragment, the actual hit SHOULD be encoded as a Data View that is encoded in a Resource Fragment.

Endpoints SHOULD always provide a links to the resource itself, i.e. each Resource or Resource Fragment SHOULD be identified by a persistent identifier or providing a URI, that is unique for Endpoint. Even if direct linking is not possible, i.e. due to licensing issues, the Endpoints SHOULD provide a URI to link to a web-page describing the corpus or collection, including instruction on how to obtain it. Endpoints SHOULD provide links that are as specific as possible (and logical), i.e. if a sentence within a resource cannot be addressed directly, the Resource Fragment SHOULD NOT contain a persistent identifier or a URI.

If the Endpoint can provide both, a persistent identifier as well as a URI, for either Resource or Resource Fragment, they SHOULD provide both. When working with results, Clients SHOULD prefer persistent identifiers over regular URIs.

Resource and Resource Fragment are serialized in XML and Endpoints MUST generate responses, that are valid according to the XML schema "Resource.xsd​" (download​). A Resource is encoded in the form of a <fcs:Resource> element, a Resource Fragment in the form of a <fcs:ResourceFragment> element. The content of a Data View is wrapped in a <fcs:DataView> element. <fcs:Resource> is the top-level element and MAY contain zero or more <fcs:DataView> elements and MAY contain zero or more <fcs:ResourceFragment> elements. A <fcs:ResourceFragment> element MUST contain one or more <fcs:DataView> elements.

The elements <fcs:Resource>, <fcs:ResourceFragment> and <fcs:DataView> MAY carry a @pid and/or a @ref attribute, which allows linking to the original data represented by the Resource, Resource Fragment, or Data View. A @pid attribute MUST contain a valid persistent identifier, a @ref MUST contain valid URI, i.e. a "plain" URI without the additional semantics of being a persistent reference.

Endpoints MUST use the identifier http://clarin.eu/fcs/resource for the responseItemType (= content for the <sru:recordSchema> element) in SRU responses.

Endpoints MAY serialize hits as multiple Data Views, however they MUST provide the Generic Hits (HITS) Data View either encoded as a Resource Fragment (if applicable), or otherwise within the Resource (if there is no reasonable Resource Fragment). Other Data Views SHOULD be put in a place that is logical for their content (as is to be determined by the Endpoint), e.g. a metadata Data View would most likely be put directly below Resource and a Data View representing some annotation layers directly around the hit is more likely to belong within a Resource Fragment.

Example 1: 

<fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource" pid="http://hdl.handle.net/4711/00-15">
  <fcs:DataView type="application/x-clarin-fcs-hits+xml">
      <!-- data view payload omitted -->
  </fcs:DataView>
</fcs:Resource>

This example shows a simple hit, which is encoded in one Data View of type Generic Hits embedded within a Resource. The type of the Data View is identified by the MIME type application/x-clarin-fcs-hits+xml. The Resource is referenceable by the persistent identifier http://hdl.handle.net/4711/08-15.

Example 2: 

<fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource" pid="http://hdl.handle.net/4711/08-15">
  <fcs:ResourceFragment>
    <fcs:DataView type="application/x-clarin-fcs-hits+xml">
      <!-- data view payload omitted -->
    </fcs:DataView>
  </fcs:ResourceFragment>
</fcs:Resource>

This example shows a hit encoded as a Resource Fragment embedded within a Resource. The actual hit is again encoded as one Data View of type Generic Hits. The hit is not directly referenceable, but the Resource, in which hit occurred, is referenceable by the persistent identifier http://hdl.handle.net/4711/08-15. In contrast to Example 1, the Endpoint decided to provide a "semantically richer" encoding and embedded the hit using a Resource Fragment within the Resource to indicate that the hit is a part of a larger resource, e.g. a sentence in a text document.

Example 3: 

<fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource"
              pid="http://hdl.handle.net/4711/08-15" ref="http://repos.example.org/file/text_08_15.html">
  <fcs:DataView type="application/x-cmdi+xml"
                pid="http://hdl.handle.net/4711/08-15-1" ref="http://repos.example.org/file/08_15_1.cmdi">
      <!-- data view payload omitted -->
  </fcs:DataView>
  <fcs:ResourceFragment pid="http://hdl.handle.net/4711/08-15-2" ref="http://repos.example.org/file/text_08_15.html#sentence2">
    <fcs:DataView type="application/x-clarin-fcs-hits+xml">
      <!-- data view payload omitted -->
    </fcs:DataView>
  </fcs:ResourceFragment>
</fcs:Resource>

The most complex example is similar to Example 2, i.e. it shows a hit is encoded as one Generic Hits Data View in a Resource Fragment, that is embedded in a Resource. In contrast to Example 2, another Data View of type CMDI is embedded directly within the Resource. The Endpoint can use this type of Data View to directly provide CMDI metadata about the Resource to Clients. All entities of the Hit can be referenced by a persistent identifier and a URI. The complete Resource is referenceable by either the persistent identifier http://hdl.handle.net/4711/08-15 or the URI http://repos.example.org/file/text_08_15.html and the CMDI metadata record in the CMDI Data View is referenceable either by the persistent identifier http://hdl.handle.net/4711/08-15-1 or the URI http://repos.example.org/file/08_15_1.cmdi. The actual hit in the Resource Fragment is also directly referenceable by either the persistent identifier http://hdl.handle.net/4711/00-15-2 or the URI http://repos.example.org/file/text_08_15.html#sentence2.

Data View

A Data View serves as a container for representing search results within CLARIN-FCS. Data Views are designed to allow for different representations of results, i.e. they are deliberately kept open to allow further extensions with more supported Data View formats. The content of a Data View is called Payload. Each Payload is typed and the type of the Payload is recorded in the @type attribute if the <fcs:DataView> element. The Payload type is is identified by a MIME type (RFC6838, RFC3023). If no existing MIME type can be used, implementors SHOULD define a properer private mime type.

The Payload of a Data View can either be deposited inline or by reference. In the case of inline, it MUST be serialized as an XML fragment below the <fcs:DataView> element. This method is the preferred methods payloads that can easily serialized in XML. In the case of by reference, the content cannot easily deposited inline, i.e. it is binary content. In this case, the Data View MUST include a @ref or @pid attribute that links location for Clients to download the payload. This location SHOULD be openly accessible, i.e. data can be downloaded freely without any need to perform a login.

For the basic profile, the Data Views Generic Hits, Component Metadata, Image and Geolocation are defined in this specification. Endpoints MAY define custom Data Views, but Clients conforming to the basic profile MAY choose to ignore them. The Generic Hits Data View is mandatory, thus all Endpoints MUST provide hits represented in the Generic Hits Data View.

NOTE: The examples in the following sections show only the payload with the enclosing <fcs:DataView> element of a Data View. Of course, the Data View must be embedded either in a <fcs:Resource> or a <fcs:ResourceFragment> element. The @pid and @ref attributes have been omitted for all inline payload types.

Generic Hits (HITS)
Description The representation of the hit
MIME type application/x-clarin-fcs-hits+xml
Payload Disposition inline

The Generic Hits Data View serves as the most basic agreement in CLARIN-FCS for serialization of search results and MUST be implemented by all Endpoints. In many cases, this Data View can only serve as an (lossy) approximation, because resources at Endpoints are very heterogeneous. E.g. the Generic Hits Data View is probably not the best representation for a hit result in a corpus of spoken language, but an architecture like CLARIN-FCS requires one common representation to be implemented by all Endpoints, therefore this Data View was defined. The Generic Hits Data View supports multiple markers for suppling highlighting for an individual hit, e.g. if a query contains a (boolean) conjunction the Endpoint can use multiple markers to provide individual highlights for the matching terms. An Endpoint MUST NOT use this Data View to aggregate several hits within one resource. Each hit SHOULD be presented within the context of a complete sentence. If that is not possible due to the nature of the type of the resource, the Endpoint MUST provide an equivalent reasonable unit of context (e.g. within a phrase of a orthographic transcription of an utterance). The <hits:Hits> element within the <hits:Result> element is not enforced by the XML schema, but Endpoints are RECOMMENDED to use it. The XML fragment of the Generic Hits payload MUST be valid according to the XML schema "DataView-Hits.xsd​" (download​).

  • Example (single hit marker): 
    <!-- potential @pid and @ref attributes omitted -->
<fcs:DataView type="application/x-clarin-fcs-hits+xml">
  <hits:Result xmlns:hits="http://clarin.eu/fcs/dataview/hits">
    The quick brown <hits:Hit>fox</hits:Hit> jumps over the lazy dog.
  </hits:Result>
</fcs:DataView>
  • Example (multiple hit markers): 
    <!-- potential @pid and @ref attributes omitted -->
<fcs:DataView type="application/x-clarin-fcs-hits+xml">
  <hits:Result xmlns:hits="http://clarin.eu/fcs/dataview/hits">
    The quick brown <hits:Hit>fox</hits:Hit> jumps over the lazy <hits:Hit>dog</hits:Hit>.
  </hits:Result>
</fcs:DataView>

Endpoint Description

Endpoints need to provide information about their capabilities to support auto-configuration of Clients, This capabilities include, among other information, the Profile that is supported by the Endpoint. The Endpoint Description mechanism provides the necessary facility to provide this information to the Clients. Endpoints MUST encode their capabilities using an XML format and embed this information into the SRU/CQL protocol as described in section Operation ''explain''. The XML fragment generated by the Endpoint for the Endpoint Description MUST be valid according to the XML schema "Endpoint-Description.xsd​" (download​).

The XML fragment for Endpoint Description is encoded as an <ed:EndpointDescription> element, that contains the following children:

  • one <ed:Profile> element (REQUIRED)
    The content of the <ed:Profile> element indicates the Profile, that is supported by the Endpoint.
    Valid values are:
    • basic: the Endpoint supports the basic Profile
    NOTE: a future CLARIN-FCS specification will introduce more values.
  • one <ed:SupportedDataViews> (REQUIRED)
    A list of Data Views, that are supported by this Endpoint. This list is composed of one or more <ed:SupportedDataView> elements. The content of a <ed:SupportedDataView> MUST be the MIME type of a supported Data View, e.g. application/x-clarin-fcs-hits+xml.
  • one <ed:Resources> element (REQUIRED)
    A list of (top-level) resources that are available, i.e. searchable, at the Endpoint. The <ed:Resources> element contains one or more <ed:Resource> elements (see below). The Endpoint MUST declare at least one (top-level) resource.

The <ed:Resource> element contains a detailed description of a resource that is available at the Endpoint. A resource is a searchable entity, e.g. a single corpus. The <ed:Resources> has a mandatory @pid attribute, that contains persistent identifier of the resource. This value MUST be the same as the MdSelfLink of the CMDI record describing the resource. The <ed:Resources> element contains the following children:

  • one or more <ed:Title> elements (REQUIRED)
    A human readable title for the resource. A REQUIRED @xml:lang attribute indicates the language of the title. An English version of the title is REQUIRED. The list of titles MUST NOT contain duplicate entries for the same language.
  • zero or more <ed:Description> elements (OPTIONAL)
    An optional human-readable description of the resource. Is SHOULD be at most one sentence. A REQUIRED @xml:lang attribute indicates the language of the description. If supplied, an English version of the description is REQUIRED. The list of descriptions MUST NOT contain duplicate entries for the same language.
  • zero or one <ed:LandingPageURI> element (OPTIONAL)
    A link to a website for the resource, e.g. a landing page for a resource, i.e. a web-site that describes a corpus.
  • one <ed:Languages> element (REQUIRED)
    The (relevant) languages available within the resource. The <ed:Languages> element contains one or more <ed:Language> elements. The content of a <ed:Language> element MUST be a ISO 639-3 three letter language code. This element should be repeated for all languages (relevant) available within the resource, however this list MUST NOT contain duplicate entries.
  • zero or one <ed:Resources> element (OPTIONAL)
    If a resource has searchable sub-resources the Endpoint MUST supply additional finer grained resource elements, which are wrapped in a <ed:Resources> element. A sub-resource is a searchable entity within a resource, e.g. a sub-corpus.

Example 4: 

<ed:EndpointDescription xmlns:ed="http://clarin.eu/fcs/endpoint-description">
  <ed:Profile>basic</ed:Profile>
  <ed:SupportedDataViews>
    <ed:SupportedDataView>application/x-clarin-fcs-hits+xml</ed:SupportedDataView>
  </ed:SupportedDataViews>
  <ed:Resources>
    <!-- just one top-level resource at the Endpoint -->
    <ed:Resource pid="http://hdl.handle.net/4711/0815">
      <ed:Title xml:lang="de">Goethe Corpus</ed:Title>
      <ed:Title xml:lang="en">Goethe Korpus</ed:Title>
      <ed:Description xml:lang="de">Der Goethe Korpus des IDS Mannheim.</ed:Description>
      <ed:Description xml:lang="en">The Goethe corpus of IDS Mannheim.</ed:Description>
      <ed:LandingPageURI>http://repos.example.org/corpus1.html</ed:LandingPageURI>
      <ed:Languages>
        <ed:Language>deu</ed:Language>
      </ed:Languages>
    </ed:Resource>
  </ed:Resources>
</ed:EndpointDescription>

This example shows a simple Endpoint Description for an Endpoint that supports the basic Profile and only provides the Generic Hits Data View. It only provides one top-level resource identified by the persistent identifier http://hdl.handle.net/4711/0815. The resource has a title as well as a description in German and English. A landing page is located at http://repos.example.org/corpus1.html. The predominant language in the resource contents is German.

Example 5: 

<ed:EndpointDescription xmlns:ed="http://clarin.eu/fcs/endpoint-description">
  <ed:Profile>basic</ed:Profile>
  <ed:SupportedDataViews>
    <ed:SupportedDataView>application/x-clarin-fcs-hits+xml</ed:SupportedDataView>
    <ed:SupportedDataView>application/x-cmdi+xml</ed:SupportedDataView>
  </ed:SupportedDataViews>
  <ed:Resources>
    <!-- top-level resource 1 -->
    <ed:Resource pid="http://hdl.handle.net/4711/0815">
      <ed:Title xml:lang="de">Goethe Corpus</ed:Title>
      <ed:Title xml:lang="en">Goethe Korpus</ed:Title>
      <ed:Description xml:lang="de">Der Goethe Korpus des IDS Mannheim.</ed:Description>
      <ed:Description xml:lang="en">The Goethe corpus of IDS Mannheim.</ed:Description>
      <ed:LandingPageURI>http://repos.example.org/corpus1.html</ed:LandingPageURI>
      <ed:Languages>
        <ed:Language>deu</ed:Language>
      </ed:Languages>
    </ed:Resource>
    <!-- top-level resource 2 -->
    <ed:Resource pid="http://hdl.handle.net/4711/0816">
      <ed:Title xml:lang="de">Mannheimer Morgen newspaper Corpus</ed:Title>
      <ed:Title xml:lang="en">Zeitungskorpus des Mannheimer Morgen</ed:Title>
      <ed:LandingPageURI>http://repos.example.org/corpus2.html</ed:LandingPageURI>
      <ed:Languages>
        <ed:Language>deu</ed:Language>
      </ed:Languages>
      <ed:Resources>
        <!-- sub-resource 1 of top-level resource 2 -->
        <ed:Resource pid="http://hdl.handle.net/4711/0816-1">
          <ed:Title xml:lang="de">Mannheimer Morgen newspaper Corpus (before 1990)</ed:Title>
          <ed:Title xml:lang="en">Zeitungskorpus des Mannheimer Morgen (vor 1990)</ed:Title>
          <ed:LandingPageURI>http://repos.example.org/corpus2.html#sub1</ed:LandingPageURI>
          <ed:Languages>
            <ed:Language>deu</ed:Language>
          </ed:Languages>
        </ed:Resource>
        <!-- sub-resource 2 of top-level resource 2 -->
        <ed:Resource pid="http://hdl.handle.net/4711/0816-2">
          <ed:Title xml:lang="de">Mannheimer Morgen newspaper Corpus (after 1990)</ed:Title>
          <ed:Title xml:lang="en">Zeitungskorpus des Mannheimer Morgen (nach 1990)</ed:Title>
          <ed:LandingPageURI>http://repos.example.org/corpus2.html#sub2</ed:LandingPageURI>
          <ed:Languages>
            <ed:Language>deu</ed:Language>
          </ed:Languages>
        </ed:Resource>
      </ed:Resources>
    </ed:Resource>
  </ed:Resources>
</ed:EndpointDescription>

This more complex example show an Endpoint Description for an Endpoint that, similar to Example 4, supports the basic profile. In addition to the Generic Hits Data View it also supports the CMDI Data View. The Endpoint has two top-level resources (identified by the persistent identifiers http://hdl.handle.net/4711/0815 and http://hdl.handle.net/4711/0816. The second top-level resource has two independently searchable sub-resources, identified by the persistent identifier http://hdl.handle.net/4711/0816-1 and http://hdl.handle.net/4711/0816-2. All resources are described using several properties, like title, description, etc.

Endpoint Custom Extensions

Endpoints can add custom extensions, i.e custom data, to the Result Format. This extension mechanism can for example be used to provide hints for an (XSLT/XQuery) application that works directly on CLARIN-FCS, e.g. to allow it to generate back and forward links to navigate in a result set.

An Endpoint MAY add arbitrary XML fragments to the extension hooks provided in the <fcs:Resource> element (see the XML schema for "Resource.xsd"). The XML fragment for the extension MUST use a custom XML namespace name for the extension. Endpoints MUST NOT use XML namespace names, that start with the prefixes http://clarin.eu, http://www.clarin.eu/, https://clarin.eu or http://www.clarin.eu/.

A Client MUST ignore any custom extensions it does not understand and skip over these XML fragments when parsing the Endpoint's response.

The appendix contains an example, how an extension could be implemented.

CLARIN-FCS to SRU/CQL binding

SRU/CQL

SRU (Search/Retrieve via URL) specifies a general communication protocol for searching and retrieving records and the CQL (Contextual Query Language) specifies a extensible query language. CLARIN-FCS is built on SRU 1.2. A subsequent specification may be built on SRU 2.0.

Endpoints and Clients MUST implement the SRU/CQL protocol suite as defined in OASIS-SRU-Overview, OASIS-SRU-APD, OASIS-CQL, SRU-Explain, SRU-Scan, especially with respect to:

  • Data Model,
  • Query Model,
  • Processing Model,
  • Result Set Model, and
  • Diagnostics Model

Endpoints and Clients MUST use the implement the APD Binding for SRU 1.2, as defined in OASIS-SRU-12. Endpoints and Clients MAY also implement APD binding for version 1.1 or version 2.0.

Endpoints and Clients MUST use the following XML namespace names (namespace URIs) for serializing responses:

  • http://www.loc.gov/zing/srw/ for SRU response documents, and
  • http://www.loc.gov/zing/srw/diagnostic/ for diagnostics within SRU response documents.

CLARIN-FCS deviates from the OASIS specification OASIS-SRU-Overview and OASIS-SRU-12 to ensure backwards comparability with SRU 1.2 services as they where defined by the LOC-SRU12.

Endpoints or Clients MUST support CQL conformance Level 2 (as defined in OASIS-CQL, section 6), i.e. be able to parse (Endpoints) or serialize (Clients) all of CQL and respond with appropriate error messages to the search/retrieve protocol interface.

NOTE: this does not imply, that Endpoints are required to support all of CQL, but rather that they are able to parse all of CQL and generate the appropriate error message, if a query includes a feature they do not support.

Endpoints MUST generate diagnostics according to OASIS-SRU-12, Appendix C for error conditions or to indicate unsupported features. Unfortunately, the OASIS specification does not provides a comprehensive list of diagnostics for CQL related errors. Therefore, Endpoints MUST use diagnostics from LOC-DIAG, section "Diagnostics Relating to CQL" for CQL related errors.

Endpoints MUST support the HTTP GET OASIS-SRU-12, Appendix B.1 and HTTP POST OASIS-SRU-12, Appendix B.2 lower level protocol binding. Endpoints MAY also support the SOAP OASIS-SRU-12, Appendix B.3 binding.

Operation explain

The explain operation of the SRU protocol serves to announce server capabilities and to allows clients to configure themselves automatically. This operation is used similarly.

The Endpoint MUST respond to a explain request by a proper explain response. As per SRU-Explain, the response MUST contain one <sru:record> element that contains an SRU Explain record. The <sru:recordSchema> element MUST contain the literal http://explain.z3950.org/dtd/2.0/, i.e. the official identifier for Explain records.

According to the Profile supported by the Endpoint the Explain record MUST contain the following elements:

Basic Profile
<zr:serverInfo> as defined in SRU-Explain (REQUIRED)
<zr:databaseInfo> as defined in SRU-Explain (REQUIRED)
<zr:schemaInfo> as defined in SRU-Explain (REQUIRED). This element MUST contain an element <zr:schema> with an @identifier attribute with a value of http://clarin.eu/fcs/resource and an @name attribute with a value of fcs.
<zr:configInfo> is OPTIONAL`
An extended profile may define how the <zr:indexInfo> element is to be used, therefore it is NOT RECOMMENDED for Endpoints to define custom extensions.
Extended Profile
NOTE: the extended profile is not yet defined and will be part of a future CLARIN-FCS specification.

To support auto-configuration in CLARIN-FCS, the Endpoint MUST provide an Endpoint Description. The Endpoint Description is included in explain response utilizing SRUs extension mechanism, i.e. by embedding an XML fragment into the <sru:extraResponseData> element. The Endpoint MUST include the Endpoint Description only if the Client performs an explain request with the extra request parameter x-fcs-endpoint-description with a value of true. If the Client performs an explain request without supplying this extra request parameter the Endpoint MUST NOT include the Endpoint Description. The format of the Endpoint Description XML fragment is defined in Endpoint Description.

The following example shows a request and response to an explain request with added extra request parameter x-fcs-endpoint-description:

  • HTTP GET request: Client ⇒ Endpoint: 
    http://repos.example.org/fcs-endpoint?operation=explain&version=1.2&x-fcs-endpoint-description=true
  • HTTP Response: Endpoint ⇒ Client: 
    <?xml version='1.0' encoding='utf-8'?>
<sru:explainResponse xmlns:sru="http://www.loc.gov/zing/srw/">
  <sru:version>1.2</sru:version>
  <sru:record>
    <sru:recordSchema>http://explain.z3950.org/dtd/2.0/</sru:recordSchema>
    <sru:recordPacking>xml</sru:recordPacking>
    <sru:recordData>
      <zr:explain xmlns:zr="http://explain.z3950.org/dtd/2.0/">
        <!-- <zr:serverInfo > is REQUIRED -->
        <zr:serverInfo protocol="SRU" version="1.2" transport="http">
          <zr:host>repos.example.org</zr:host>
          <zr:port>80</zr:port>
          <zr:database>sru</zr:database>
        </zr:serverInfo>
        <!-- <zr:databaseInfo> is REQUIRED -->
        <zr:databaseInfo>
          <zr:title lang="de">Goethe Corpus</zr:title>
          <zr:title lang="en" primary="true">Goethe Korpus</zr:title>
          <zr:description lang="de">Der Goethe Korpus des IDS Mannheim.</zr:description>
          <zr:description lang="en" primary="true">The Goethe corpus of IDS Mannheim.</zr:description>
        </zr:databaseInfo>
        <!-- <zr:configInfo> is REQUIRED -->
        <zr:schemaInfo>
          <zr:schema identifier="http://clarin.eu/fcs/1.0" name="fcs">
            <zr:title lang="en" primary="true">CLARIN Federated Content Search</zr:title>
          </zr:schema>
        </zr:schemaInfo>
        <!-- <zr:configInfo> is OPTIONAL -->
        <zr:configInfo>
          <zr:default type="numberOfRecords">250</zr:default>
          <zr:setting type="maximumRecords">1000</zr:setting>
        </zr:configInfo>
      </zr:explain>
    </sru:recordData>
  </sru:record>
  <!-- <sru:echoedExplainRequest> is OPTIONAL -->
  <sru:echoedExplainRequest>
    <sru:version>1.2</sru:version>
    <sru:baseUrl>https://clarin.ids-mannheim.de/digibibsru</sru:baseUrl>
  </sru:echoedExplainRequest>
  <sru:extraResponseData>
    <ed:EndpointDescription xmlns:ed="http://clarin.eu/fcs/endpoint-description">
      <ed:Profile>basic</ed:Profile>
      <ed:SupportedDataViews>
        <ed:SupportedDataView>application/x-clarin-fcs-hits+xml</ed:SupportedDataView>
      </ed:SupportedDataViews>
      <ed:Resources>
        <!-- just one top-level resource at the Endpoint -->
        <ed:Resource pid="http://hdl.handle.net/4711/0815">
          <ed:Title xml:lang="de">Goethe Corpus</ed:Title>
          <ed:Title xml:lang="en">Goethe Korpus</ed:Title>
          <ed:Description xml:lang="de">Der Goethe Korpus des IDS Mannheim.</ed:Description>
          <ed:Description xml:lang="en">The Goethe corpus of IDS Mannheim.</ed:Description>
          <ed:LandingPageURI>http://repos.example.org/corpus1.html</ed:LandingPageURI>
          <ed:Languages>
            <ed:Language>deu</ed:Language>
          </ed:Languages>
        </ed:Resource>
      </ed:Resources>
    </ed:EndpointDescription>
  </sru:extraResponseData>
</sru:explainResponse>

Operation scan

The scan operation of the SRU protocol is currently not used in the basic profile of CLARIN-FCS. An extended profile may use this operation, therefore it NOT RECOMMENDED for Endpoints to define custom extensions that use this operation.

Operation searchRetrieve

The searchRetrieve operation of the SRU protocol is used for searching in the Resources that are provided by the Endpoint. The SRU protocol defines the serialization of request and response formats in OASIS-SRU-12. In SRU, search result hits are encoded down to a record level, i.e. the <sru:record> element, and SRU allows records to be serialized in various formats, so called record schemas.

Endpoints MUST support the CLARIN-FCS record schema (see section Result Format) and MUST use the value http://clarin.eu/fcs/resource for the responseItemType ("record schema identifier"). Endpoints MUST represent exactly one hit within the Resource as one SRU record, i.e. <sru:record> element.

The following example shows a request and response to an searchRetrieve request with a term-only query for "cat":

  • HTTP GET request: Client ⇒ Endpoint: 
    http://repos.example.org/fcs-endpoint?operation=searchRetrieve&version=1.2&query=cat
  • HTTP Response: Endpoint ⇒ Client: 
    <?xml version='1.0' encoding='utf-8'?>
<sru:searchRetrieveResponse xmlns:sru="http://www.loc.gov/zing/srw/">
  <sru:version>1.2</sru:version>
  <sru:numberOfRecords>6</sru:numberOfRecords>
  <sru:records>
    <sru:record>
      <sru:recordSchema>http://clarin.eu/fcs/resource</sru:recordSchema>
      <sru:recordPacking>xml</sru:recordPacking>
      <sru:recordData>
        <fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource" pid="http://hdl.handle.net/4711/08-15">
          <fcs:ResourceFragment>
            <fcs:DataView type="application/x-clarin-fcs-hits+xml">
              <hits:Result xmlns:hits="http://clarin.eu/fcs/1.0/hits">
                The quick brown <hits:Hit>cat</hits:Hit> jumps over the lazy dog.
              </hits:Result>
            </fcs:DataView>
          </fcs:ResourceFragment>
        </fcs:Resource>
      </sru:recordData>
      <sru:recordPosition>1</sru:recordPosition>
    </sru:record>
    <!-- more <sru:records> omitted for brevity -->
  </sru:records>
  <sru:echoedSearchRetrieveRequest>
    <sru:version>1.2</sru:version>
    <sru:query>cat</sru:query>
    <sru:xQuery xmlns="http://www.loc.gov/zing/cql/xcql/">
      <searchClause>
        <index>cql.serverChoice</index>
        <relation>
          <value>=</value>
        </relation>
        <term>cat</term>
      </searchClause>
    </sru:xQuery>
    <sru:startRecord>1</sru:startRecord>
    <sru:baseUrl>http://repos.example.org/fcs-endpoint</sru:baseUrl>
  </sru:echoedSearchRetrieveRequest>
</sru:searchRetrieveResponse>

In general, the Endpoint is REQUIRED to accept an unrestricted search and then SHOULD perform the search operation on all Resources, that are available at the Endpoint. If that is for some reason not feasible, e.g. performing an unrestricted search would allocate too many resources, the Endpoint MAY independently restrict the search to a scope that it can handle. If it does so, it MUST issue a non-fatal diagnostics http://clarin.eu/fcs/diagnostic/2 ("Resource set too large. Query context automatically adjusted."). The details field of diagnostics MUST contain a comma separated list of persistent identifiers of the resources to which the query scope was limited.

The Client can request the Endpoint to restrict the search to a sub-resource of these Resources. In this case, the Client MUST pass a comma-separated list of persistent identifiers in the x-fcs-context extra request parameter of the searchRetrieve request. The Endpoint MUST then restrict the search to those Resources, that are identified by the persistent identifiers passed by the Client. If a Client requests too many resources for the Endpoint to handle with x-fcs-context, the Endpoint MAY issue a fatal diagnostic http://clarin.eu/fcs/diagnostic/3 ("Resource set too large. Cannot perform Query.") and terminate processing. Alternatively, the Endpoint MAY also automatically adjust the scope and issue a non-fatal diagnostic http://clarin.eu/fcs/diagnostic/2 (see above). And Endpoint MUST NOT issue a http://clarin.eu/fcs/diagnostic/3 diagnostic in response to a request, if a Client performed the request without the x-fcs-context extra request parameter.

The Client can extract all valid persistent identifiers from the @pid attribute of the <ed:Resource> element, obtained by the explain request (see section Operation ''explain'' and section Endpoint Description). The list of persistent identifiers can get extensive, but an Client can use the HTTP POST method instead of HTTP GET method for submitting the request.

For example, to restrict the search to the Resource with the persistent identifier http://hdl.handle.net/4711/0815 the Client must issue the following request: 

http://repos.example.org/fcs-endpoint?operation=searchRetrieve&version=1.2&query=cat&x-fcs-context=http://hdl.handle.net/4711/0815

To restrict the search to the Resources with the persistent identifier http://hdl.handle.net/4711/0815 and http://hdl.handle.net/4711/0816-2 the Client must issue the following request: 

http://repos.example.org/fcs-endpoint?operation=searchRetrieve&version=1.2&query=cat&x-fcs-context=http://hdl.handle.net/4711/0815,http://hdl.handle.net/4711/0816-2

If an invalid persistent identifier is passed by the Client, the Endpoint MUST issue a http://clarin.eu/fcs/diagnostic/1 diagnostic, i.e add the appropiate XML fragment to the <sru:diagnostics> element of the response. The Endpoint MAY treat this condition as fatal, i.e. just issue the diagnostic and perform no search or it MAY treat it a non-fatal and perform the search.

Normative Appendix

List of extra request parameters

The following extra request parameters are used in CLARIN-FCS. The column SRU operations list the SRU operation, for which this extra request parameter is to be used. Clients MUST NOT use the parameter for an operation that is not listed in this column. However, if a Client does so an Endpoint MAY issue a fatal "Unsupported Parameter" (info:srw/diagnostic/1/8) diagnostic.

Parameter Name SRU operations Allowed values Description
x-fcs-endpoint-description explain true; all other values are reserved and MUST not be used by Clients If present, the Endpoint MUST include an Endpoint Description in the <sru:extraResponseData> element of the explain response.
x-fcs-context searchRetrieve A comma separated list of persistent identifiers The Endpoint MUST restrict the search to the resources identified by the persistent identifiers.

List of diagnostics

Apart from the SRU diagnostics defined in OASIS-SRU-12, Appendix C and LOC-DIAG, the following diagnostics are used in CLARIN-FCS. The "Details Format" column specifies what SHOULD be returned in the details field. If this column is blank, the format is "undefined" and the Endpoint MAY return whatever it feels appropriate, including nothing.

Identifier URI Description Details Format
http://clarin.eu/fcs/diagnostic/1 Persistent identifier passed in for restricting the search is invalid The offending persistent identifier
http://clarin.eu/fcs/diagnostic/2 Resource set too large. Query context automatically adjusted. A comma separated list of persistent identifiers of the resources to which the query scope was limited.
http://clarin.eu/fcs/diagnostic/3 Resource set too large. Cannot perform Query.

Non-normative Appendix

The following sections are non-normative.

Referring to an Endpoint from a CMDI record

Centers are encouraged to provide links to their CLARIN-FCS Endpoints in the metadata records for their resources. Other services, like the VLO, can use this information for automatically configuring an Aggregator for searching resources at the Endpoint. To refer to an Endpoint a <cmdi:ResourceProxy> with <cmdi:ResourceType> set to the value SearchService and a @mimetype attribute with a value of application/sru+xml need to be added to the CMDI record. The content of the <cmdi:ResourceRef> element must contain a URI that points to the Endpoint web service.

Example: 

<cmdi:CMD xmlns:cmdi="http://www.clarin.eu/cmd/" CMDVersion="1.1">
  <cmdi:Header>
    <!-- ... -->
    <cmdi:MdSelfLink>http://hdl.handle.net/4711/0815</cmdi:MdSelfLink>
    <!-- ... -->
  </cmdi:Header>
  <cmdi:Resources>
    <cmdi:ResourceProxyList>
      <!-- ... -->
      <cmdi:ResourceProxy id="r4711">
        <cmdi:ResourceType mimetype="application/sru+xml">SearchService</cmdi:ResourceType>
        <cmdi:ResourceRef>http://repos.example.org/fcs-endpoint</cmdi:ResourceRef>
      </cmdi:ResourceProxy>
      <!-- ... -->
    </cmdi:ResourceProxyList>
  </cmdi:Resources>
  <!-- ... -->
</cmdi:CMD>

Endpoint custom extensions

The CLARIN-FCS protocol specification allows Endpoints to add custom data to their responses, e.g. to provide hints to for an (XSLT/XQuery) application that works directly on CLARIN-FCS. It could use the custom data to generate back and forward links for a GUI to navigate in a result set.

The following example illustrates how extensions can be embedded into the Result Format: 

<fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource" pid="hdl:4711/0815">
    <fcs:DataView type="application/x-clarin-fcs-hits+xml">
      <hits:Result xmlns:hits="http://clarin.eu/fcs/dataview/hits">
        The quick brown <hits:Hit>fox</hits:Hit> jumps over the lazy <hits:Hit>dog</hits:Hit>.
      </hits:Result>
    </fcs:DataView>
    
    <!--
        NOTE: this is purly fictional and only serves to demonstrate how
              to add custom extensions to the result representation
              within CLARIN-FCS.
    -->

    <!--
        Example 1: a hypothetical Endpoint extension for navigation in a result
        set: it basically provides a set of hrefs, that a GUI can convert into
        navigation buttions.    
    -->
    <nav:navigation xmlns:nav="http://repos.example.org/navigation">
        <nav:curr href="http://repos.example.org/resultset/4711/4611" />
        <nav:prev href="http://repos.example.org/resultset/4711/4610" />
        <nav:next href="http://repos.example.org/resultset/4711/4612" />
    </nav:navigation>

    <!--
       Example 2: a hypothetical Endpoint extension for directly referencing parent
       resources: if basically provides a link to the parent resource, that can be
       exploited by an GUI (e.g. build on XSLT/XQuery).
    -->
    <parent:Parent xmlns:parent="http://repos.example.org/parent"
                   ref="http://repos.example.org/path/to/parent/1235.cmdi" />
</fcs:Resource>

Endpoint highlight hints for repositories

An Aggregator can use the @href attributes of the <fcs:Resource>, <fcs:ResourceFragment> or <fcs:DataView> elements to provide a link for the user to directly jump to the resource at an Repository. To support hit highlighting, an Endpoint can augment the URI in the @ref attribute with query parameters to implement hit highlighting in the Repository.

In the following example, the URI http://repos.example.org/resource.cgi/<pid> is a CGI script, that displays a given resource at the Repository in HTML format and uses the highlight query parameter to add highlights to the resource. Of course, it's up to the Endpoint and the Repository, if and how they implement such a feature. 

<fcs:Resource xmlns:fcs="http://clarin.eu/fcs/resource" pid="hdl:4711/0815">
  <fcs:DataView type="application/x-clarin-fcs-hits+xml" ref="http://repos.example.org/resource.cgi/4711/0815?highlight=fox">
    <hits:Result xmlns:hits="http://clarin.eu/fcs/dataview/hits">
      The quick brown <hits:Hit>fox</hits:Hit> jumps over the lazy dog.
    </hits:Result>
  </fcs:DataView>
</fcs:Resource>

Proposal for new specification: Federated Content Search - Data Views

The following is a proposal for the separate specification of Data Views for CLARIN-FCS. When done, cut and paste to the appropriate section of the Wiki and publish on the CLARIN web page.

CLARIN Federated Content Search (CLARIN-FCS) - Data Views

  1. FCS Specification Scrapbook
    1. Issues with current document
    2. General ideas / design goals towards better specification
    3. TODOs for the current draft / Preliminary items identified by …
    4. Proposal for new specification: Federated Content Search - Core …
  2. CLARIN Federated Content Search (CLARIN-FCS) - Core
    1. Introduction
      1. Terminology
      2. Glossary
      3. Normative References
      4. Non-Normative References
      5. Typographic and XML Namespace conventions
    2. CLARIN-FCS Interface Specification
      1. Capabilities and Profiles
      2. Result Format
        1. Resource and ResourceFragment
        2. Data View
          1. Generic Hits (HITS)
      3. Endpoint Description
      4. Endpoint Custom Extensions
    3. CLARIN-FCS to SRU/CQL binding
      1. SRU/CQL
      2. Operation explain
      3. Operation scan
      4. Operation searchRetrieve
    4. Normative Appendix
      1. List of extra request parameters
      2. List of diagnostics
    5. Non-normative Appendix
      1. Referring to an Endpoint from a CMDI record
      2. Endpoint custom extensions
      3. Endpoint highlight hints for repositories
    6. Proposal for new specification: Federated Content Search - Data Views
  3. CLARIN Federated Content Search (CLARIN-FCS) - Data Views
    1. Introduction
      1. Terminology
      2. Normative References
      3. Non-Normative References
      4. Typographic and XML Namespace conventions
    2. Data Views
      1. Generic Hits (HITS)
      2. Component Metadata (CMDI)
      3. Images (IMG)
      4. Geolocation (GEO)
  4. Discussion

Introduction

This specification is a supplementary specification to the CLARIN-FCS Core specification and defines additional Data View to be used in CLARIN-FCS. This specification will tersely describe the supplementary Data Views. For detailed information about the CLARIN-FCS interface specification see CLARIN-FCS-Core.

Terminology

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in RFC2119.

Normative References

RFC2119
Key words for use in RFCs to Indicate Requirement Levels, IETF RFC 2119, March 1997,
​http://www.ietf.org/rfc/rfc2119.txt
XML-Namespaces
Namespaces in XML 1.0 (Third Edition), W3C, 8 December 2009,
​http://www.w3.org/TR/2009/REC-xml-names-20091208/
CLARIN-FCS-Core
CLARIN Federated Content Search (CLARIN-FCS) - Core, SCCTC FCS Task Force, March 2014,
​http://www.clarin.eu/fcs/add/link/here

Non-Normative References

RFC6838
Media Type Specifications and Registration Procedures, IETF RFC 6838, January 2013,
​http://www.ietf.org/rfc/rfc6838.txt
RFC3023
XML Media Types, IETF RFC 3023, January 2001,
​http://www.ietf.org/rfc/rfc3023.txt
KML
Keyhole Markup Language (KML), Open Geospatial Consortium, 2008,
​http://www.opengeospatial.org/standards/kml

Typographic and XML Namespace conventions

The following typographic conventions for XML fragments will be used throughout this specification:

  • <prefix:Element>
    An XML element with the Generic Identifier Element that is bound to an XML namespace denoted by the prefix prefix.
  • @attr
    An XML attribute with the name attr
  • string
    The literal string must be used either as element content or attribute value.

Endpoints and Clients MUST adhere the XML-Namespaces specification. The CLARIN-FCS interface specification generally does not dictate whether XML elements should be serialized in their prefixed or non-prefixed syntax, but Endpoints MUST ensure that the correct XML namespace is used for elements and that XML namespaces are declared correctly. Clients MUST be agnostic to which syntax for serializing the XML elements, i.e. if the prefixed or un-prefixed variant was used, and SHOULD operate solely on expanded names, i.e. pairs of namespace name and local name.

The following XML namespace names and prefixes are used throughout this specification. The column "Recommended Syntax" indicates, which syntax variant SHOULD be used by the Endpoint to serialize the XML response.

Prefix Namespace Name Comment Recommended Syntax
fsc http://clarin.eu/fcs/resource CLARIN-FCS Resources prefixed
cmdi http://www.clarin.eu/cmd/ Component Metadata un-prefixed
kml http://www.opengis.net/kml/2.2 Keyhole Markup Language un-prefixed

Data Views

A Data View serves as a container for representing search results within CLARIN-FCS. Data Views are designed to allow for different representations of results. This specification defines supplementary Data Views beyond the Generic Hits Data View, that is part of the CLARIN-FCS Core specification. For detailed information what Data Views are and how they are integrated in CLARIN-FCS see CLARIN-FCS-Core.

NOTE: The examples in the following sections show only the payload with the enclosing <fcs:DataView> element of a Data View. Of course, the Data View must be embedded either in a <fcs:Resource> or a <fcs:ResourceFragment> element. The @pid and @ref attributes have been omitted for all inline payload types.

Generic Hits (HITS)

The Generic Hits (HITS) Data View is an integral part of the Core specification and serves as the as the most basic agreement in CLARIN-FCS for the serialization of search results. For details about this Data View, see refer to the Core specification CLARIN-FCS-Core, Section "Generic Hits (HITS)".

Component Metadata (CMDI)

Description A CMDI metadata record
MIME type application/x-cmdi+xml
Payload Disposition inline or reference

The Component Metadata Data View allows to embed a CMDI metadata record that is applicable to the specific context into the Endpoint response, e.g. metadata about the resource in which the hit was produced. If this CMDI record is applicable for the entire Resource, it SHOULD be put in a <fcs:DataView> element below the <fcs:Resource> element. If it is applicable to the Resource Fragment, i.e. it contains more specialized metadata than the metadata for the encompassing resource, it SHOULD be put in a <fcs:DataView> element below the <fcs:ResourceFragment> element. Endpoints SHOULD provide the payload inline, but Endpoints MAY also use the reference method. If an Endpoint uses the reference method, the CMDI metadata record MUST be downloadable without any restrictions.

  • Example (inline): 
    <!-- potential @pid and @ref attributes omitted -->
<fcs:DataView type="application/x-cmdi+xml">
  <cmdi:CMD xmlns:cmdi="http://www.clarin.eu/cmd/" CMDVersion="1.1">
    <!-- content omitted -->
  </cmdi:CMD>
</fcs:DataView>
  • Example (referenced): 
    <!-- potential @pid attribute omitted -->
<fcs:DataView type="application/x-cmdi+xml" ref="http://repos.example.org/resources/4711/0815.cmdi" />

Images (IMG)

Description An image related to the hit
MIME type image/png, image/jpeg, image/gif, image/svg+xml
Payload Disposition reference

The Image Data View allows to provide an image, that is relevant to the hit, e.g. a facsimile of the source of a transcription. Endpoints MUST provide the payload by the reference method and the image file SHOULD be downloadable without any restrictions.

  • Example: 
    <!-- potential @pid attribute omitted -->
<fcs:DataView type="image/png" ref="http://repos.example.org/resources/4711/0815.png" />

Geolocation (GEO)

Description An geographic location related to the hit
MIME type application/vnd.google-earth.kml+xml
Payload Disposition inline

The Geolocation Data View allows to geolocalize a hit. If MUST be encoded using the XML representation of the Keyhole Markup Language (KML). The KML fragment MUST comply with the specification as defined by KML.

  • Example: 
    <!-- potential @pid and @ref attributes omitted -->
<fcs:DataView type="application/vnd.google-earth.kml+xml">
  <kml:kml xmlns:kml="http://www.opengis.net/kml/2.2">
    <kml:Placemark>
      <kml:name>IDS Mannheim</kml:name>
      <kml:description>Institut für Deutsche Sprache, R5 6-13, 68161 Mannheim, Germany</kml:description>
      <kml:Point>
        <kml:coordinates>8.4719510,49.4883700,0</kml:coordinates>
      </kml:Point>
    </kml:Placemark>
  </kml:kml>
</fcs:DataView>

Discussion

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