NOTE: This page is work-in-progress. Final draft is scheduled to be delivered by 2015-10-31.

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 attr
• string
  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

The Advanced Search capability allows searching in annotated data. Queries can be across annotation layer, e.g. token and part-of-speech layer. CLARIN-FCS defined a set of search-able annotation layers with certain semantics and syntax. Endpoints SHOULD support as many different, of course depending n the resource type, annotation layers as possible.

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	SAMPA	"'du:", "'vi:-d6 'ha:-b@n"
text	Annotation tier that is used in Basic Search	String	"Dog", "cat" "walked"

The column Syntax describes the inventory of symbols that a Client MUST use with a corresponding annotation layer; the value String denotes that symbols are arbitrary Unicode Strings, i.e. no fixed inventory of symbols are defined. An Endpoint SHOULD provide an appropriate error, if a Client used an invalid value.

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.