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CLARIN Federated Content Search (CLARIN-FCS) - Core 2.0
Introduction
TODO: Proof-read/Check sub-sections.
The goal of the CLARIN Federated Content Search (CLARIN-FCS) - Core specification is to introduce an 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, which 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 domain specific language for representing queries to information retrieval systems such as search engines, bibliographic catalogs and museum collection information.
- 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.
- Endpoint
- A software component, which implements the CLARIN-FCS interface specification and translates between CLARIN-FCS and a search engine.
- FCS-QL
- Federated Content Search Query Language is the query language used in the advanced CLARIN-FCS profile. It is derived from Corpus Workbench's CQP-TUTORIAL
- Hit
- A piece of data returned by a Search Engine that matches the search criterion. What is considered a Hit highly depends on Search Engine.
- Interface Specification
- Common harmonized interface and suite of protocols that repositories need to implement.
- 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 Repositories and their Endpoints and provides information about these to other components, e.g. an Aggregator. The CLARIN Center Registry is an implementation of such a repository registry.
- Resource
- A searchable and addressable entity at an Endpoint, such as a text corpus or a multi-modal corpus.
- Resource Fragment
- A smaller unit in a Resource, i.e. a sentence in a text corpus or a time interval in an audio transcription.
- Result Set
- An (ordered) set of hits that match a search criterion produced by a search engine as the result of processing a query.
- 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. Originally introduced by Library of Congress LOC-SRU12, later standardization process moved to OASIS OASIS-SRU12.
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
- UD-POS
-
Universal Dependencies, Universal POS tags,
https://universaldependencies.github.io/docs/u/pos/index.html
- SAMPA
- Dafydd Gibbon, Inge Mertins, Roger Moore (Eds.): Handbook of Multimodal and Spoken Language Systems. Resources, Terminology and Product Evaluation, Kluwer Academic Publishers, Boston MA, 2000, ISBN 0-7923-7904-7
- CLARIN-FCS-DataViews
-
CLARIN Federated Content Search (CLARIN-FCS) - Data Views, SCCTC FCS Task-Force, April 2014,
https://trac.clarin.eu/wiki/FCS/Dataviews
Non-Normative References
- CQP-TUTORIAL
-
Evert et al.: The IMS Open Corpus Workbench (CWB) CQP Query Language Tutorial, CWB Version 3.0, February 2010,
http://cwb.sourceforge.net/files/CQP_Tutorial/
- 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 attrstring
The literal string must be used either as element content or attribute value.
Endpoints and Clients MUST
adhere to 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 regarding 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 |
---|---|---|---|
fcs | 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 Data View | prefixed |
adv | http://clarin.eu/fcs/dataview/advanced | CLARIN-FCS Advanced Data View | 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 |
Careful with the SRU Namespaces; they probably need to be adjusted SRU 2.0 (=> OASIS).
CLARIN-FCS Interface Specification
The CLARIN-FCS Interface Specification defines a set of capabilities, 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.
Specifically, the CLARIN-FCS Interface Specification consists of two parts, a set of formats, and a transport protocol. The Endpoint component is a software component that acts as a bridge between a Client and a Search Engine and passes the requests sent by the Client to the Search Engine. The Search Engine is a custom software component that allows the search of language resources in a Repository. The Endpoint implements the Transport Protocol and acts as a mediator between the CLARIN-FCS specific formats and the idiosyncrasies of Search Engines of the individual Repositories. The following figure illustrates the overall architecture:
+---------+ | Client | +---------+ /|\ | | SRU / CQL | w/CLARIN-FCS extensions | \|/ +----------------------------------------------+ | | Endpoint /|\ | | | | | | ------------------- ------------------- | | | translate request | | translate result | | | ------------------- ------------------- | | | | | | \|/ | | +----------------------------------------------+ /|\ | | Search Engine specific protocols/formats | \|/ +---------------------------+ | 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 or FCS-QL to the query 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 them to the Client.
Discovery
The Discovery step allows a Client to gather information about an Endpoint, in particular which capabilities are supported or which resources are available for searching.
Capabilities
A Capability defines a certain feature set that is part of CLARIN-FCS, e.g. what kind of queries are supported. Each Endpoint implements some (or all) of these Capabilities. The Endpoint will announce the capabilities it provides to allow a Client to auto-tune itself (see section Endpoint Description). Each Capability is identified by a Capability Identifier, which uses the URI syntax. The following Capabilities are defined in CLARIN-FCS defined:
Name | Capability Identifier | Summary |
---|---|---|
Basic Search | http://clarin.eu/fcs/capability/basic-search | Simple full-text searching |
Advanced Search | http://clarin.eu/fcs/capability/advanced-search | Searching in structured and/or annotated data |
Endpoints MUST
implement the Basic Search Capability. Endpoints MUST NOT
invent custom Capability Identifiers and MUST
only use the values defined above.
Endpoint Description
Add stuff required for advanced capability.
Searching
In the Searching step the Client performs the actual search request to a to previously discovered Endpoint.
Basic Search
The Basic Search capability provides simple full-text search. Queries in Basic Search MUST
be performed in the Contextual Query Language (OASIS-CQL). The Endpoint MUST
support term-only queries. The Endpoint SHOULD
support terms combined with boolean operator queries (AND and OR), including sub-queries. An Endpoint MAY
also support NOT or PROX operator queries. If an 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 (LOC-DIAG).
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.
Examples for valid CQL queries for Basic Search are:
cat "cat" cat AND dog "grumpy cat" "grumpy cat" AND dog "grumpy cat" OR "lazy dog" cat AND (mouse OR "lazy dog")
NOTE: In CQL, a term can be a single token or a phrase, i.e. tokens separated by spaces. If a single term contains spaces, it needs to be quoted.
NOTE: Endpoints MUST
be able to parse all of CQL. If they don't support a certain CQL feature, they MUST
generate an appropriate error message (see section SRU/CQL). Especially, if an Endpoint only supports Basic Search, 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.
Advanced Search
About advanced search
Layers
Identifier | Annotation Tier Description | Syntax | Examples (without quotes) |
---|---|---|---|
token | Appropriate tokenisation of resource, i.e. words | String | "Dog", "cat", "walked" |
lemma | Lemmatisation of tokens | String | "good", "walking", "dog" |
pos | Part-of-Speech annotations | Universal POS tags | "NOUN", "VERB", "ADJ" |
orth | Orthographic transcription of (mostly) spoken resources | String | "dug", "cat", "wolking" |
norm | Orthographic normalization of (mostly) spoken resources | String | "dog", "cat", "walking" |
phonetic | Phonetic transcription | Speech Assessment Methods Phonetic Alphabet (SAM-PA) | "'du:", "'vi:-d6 'ha:-b@n" |
ne | Named entities | String | "Utrecht", "Poland", "Felix the Cat" |
text | Annotation tier that is used in Basic Search | String | "Dog", "cat" "walked" |
FCS-QL
About available layers
Result Format
Resource and ResourceFragment
Data View
Generic Hits (HITS)
Advanced (ADV)
New section.
"Versioning and Extensions"
"Backwards compatibility statements"
Say something about backwards compatibility with "basic-search".
Clients should also be compatible with FCS 1.0 (= SRU 1.2) and use heuristic to determine, if an endpoint is still using FCS 1.0.
Endpoint Custom Extensions
Talk about extensions in general; this section needs to stay in normative part due to the namespace stuff
CLARIN-FCS to SRU/CQL binding
SRU/CQL
SRU 2.0 requirement
Operation explain
Basically stays the same, but adjust for advanced stuff.
Operation scan
Basically stays the same, but adjust for advanced stuff (if required).
Operation searchRetrieve
Align with newly introduced section "Search Phase"
Define String for SRU query-lanaguge paramater ("fcs"? "clarin-fcs"?)
Normative Appendix
List of extra request parameters
Revisit and update as required; don't forget to add the new request parameter ("allow rewriting" => allow endpoint to trade precision in favor of recall).
List of diagnostics
Revisit and update as required; don't forget to add the 4 new diagnostics.
Non-normative Appendix
Syntax variant for Handle system Persistent Identifier URIs
Referring to an Endpoint from a CMDI record
Endpoint custom extensions
Endpoint highlight hints for repositories
All sections to be updated as required / maybe check if something should be deleted.
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