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CEN SQI - Overview
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Terms of use
These contents have been obtained from the European Committee for Standardization (CEN) official Web site and edited for presentation. Please refer to the CEN official Web site for additional information on terms of use.
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European Commitee for Standardization
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The Simple Query Interface (SQI) specification, supported by CEN WS-LT (CWA 15454:2005), presents an Application Programming Interface (API) for querying learning object repositories. Since one major design objective is to keep the specification simple and easy to implement, the interface is labelled Simple Query Interface (SQI).
In the context of SQI, learning object repositories are defined as collections of educational material, courses, and learning objects with associated descriptions (referred to as “metadata”). Examples of repositories for learning are educational brokers, knowledge pools, streaming video servers, etc.
The collaborative effort of combining highly heterogeneous repositories has led to the following requirements:- SQI is neutral in terms of results format and query languages. The repositories connecting via SQI can be of highly heterogeneous nature, therefore, SQI makes no assumptions about the query language or results format.
- SQI supports Synchronous and Asynchronous Queries in order to allow application of the SQI specification in heterogeneous use cases.
- SQI supports, both, a stateful and a stateless implementation.
- SQI is based on a session management concept in order to separate authentication issues from query management.
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The design of the API itself is based on following design principles:- Command-Query Separation Principle,
- Simple Command Set and Extensibility.
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| SQI forms a key part of the infrastructure used by the ASPECT project. ASPECT will also develop mappings from SQI to other search specifications including SRU.Simple Query Interface specification |
Terms of use
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These contents have been obtained from the European Committee for Standardization (CEN) official Web site and edited for presentation. Please refer to the CEN official Web site for additional information on terms of use.
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The Simple Query Interface specification defines a number of methods that can be used by a source (a particular application) for configuring and submitting queries to a target system (a repository of learning objects) and retrieving results from it.
UML Class Diagram of the Simple Query Interface
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SQI can be deployed in two different scenarios:- In the synchronous scenario, the target returns the query results to the source. Results retrieval is therefore initiated by the source through the submission of the query and through other methods allowing the source to access the query results.
- In the asynchronous scenario, results retrieval is target-initiated. Whenever a significant amount of matching results is found, these results are forwarded to the source by the target. To support this communication the source must implement a results listener. The source must be able to uniquely identify a query sent to a particular target (even if the same query is sent to multiple targets). Otherwise the source is not able to distinguish the search results retrieved from various targets and/or queries previously submitted to a target.
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The SQI methods can be divided into three groups:
1. Configuration Methods:- setQueryLanguage: This method allows the source to control the syntax used in the query statement by identifying the query language.
- setMaxQueryResults: This method defines the maximum number of results, which a query will produce.
- setMaxDuration: This method enables the source to set a time-out for the query in case of an asynchronously operated query interface.
- setResultsFormat: This method allows the source to control the format of the results returned by the target.
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2. Synchronous Query Methods- setResultsSetSize: This method defines the maximum number of results, which will be returned by a single results set.
- synchronousQuery: This method places a query at the target. Within a session multiple queries can be submitted simultaneously. The method returns a set of metadata records matching
- the query.
- getTotalResultsCount: This method returns the total number of available results of a query.
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3. Asynchronous Query Methods- setSourceLocation: This method is required to be called before a query is submitted in asynchronous mode. The parameter sourceLocation specifies the location of the source’s results listener in order for
- the target to be able to send the results. The sourceLocation must be an URL.
- asynchronousQuery: This method allows the source to submit a query to the target, while the results are returned in an asynchronous method. A query ID issued by the source is required in order to link the query results with the query, when they are later returned using the results listener. By using unique query IDs it is possible to submit an arbitrary number of queries per active session. Due to the asynchronous nature of this method, query results could still arrive from previous queries.
- queryResultsListener: This target-initiated method forwards the results sets to the source. The queryID parameter isused for linking the query results to previously submitted query, when they are later return using the results listener.
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Query Language and Results Format
In order to make use of SQI to implement full query functionality, SQI needs to be complemented with agreements about:- the set of attributes and vocabularies that can be used in the query,
- the query language and its representation,
- the representation of list of learning objects that satisfy the query, and
- the representation of individual metadata instances on learning objects.
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SQI is agnostic on these issues: Any agreement between two or more repositories is valid for SQI. Such agreements can, for example, be expressed by XML schemas or RDF schemas.
Although SQI does not directly contribute to overcome the differences of the various paradigms in metadata management (Z39.50, XML-based approaches, RDF community), it aims to become an independent specification for all open educational repositories. |
Terms of use
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These contents have been obtained from the European Committee for Standardization (CEN) official Web site and edited for presentation. Please refer to the CEN official Web site for additional information on terms of use.
Print
Title: CWA 15454:2005 - A Simple Query Interface Specification for Learning Repositories
Version: 1.0
Release Date: November 2005
Editor: Bernd Simon, Erik Duval, David Massart, Frans Van Assche, Stefaan Ternier
Status: Official CEN Workshop Agreement
Electronic version: Available in pdf format. |
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