Output Query Format

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The part of the standard specifying the structure of the result set as well as carrying

messages like errors or announcements is called the Output Query Format. The outermost

XML element Output can envelope the GlobalComment, SystemMessage and ResultItem

child elements.

To describe the result of the query one can use GlobalComment. To propagate information

regarding the responder system, the SystemMessage element is utilized. This includes

errors and exception - for example if a proper result set cannot be composed - as well as

status messages.

The ResultItem element deVnes a single result returned by the MPQF service. It contains

a unique identiVer18 and information about ranking and similarity of the result regarding

the submitted query. A possible response to the query introduced in listing 2.3 is shown

in listing 2.4. The result items provide both the desired description using Dublin Core

metadata as well as Uniform Resource IdentiVers linking to the actual content.

Additionally the Output Query Format has means to serve a client’s wish to receive the

result set divided into one or more individual pages. For each virtual page a new MPQF

instance document is created and returned. To navigate within the pages the service

provider assigns attributes decoding the current page and the total page count.

18An identiVer is needed to provide the content service with feedback using the QueryByRelevanceFeedback

query type

14 of 55 Chapter 2. Related Background

Listing 2.4: A possible response of a MPQF aware content provider

2.2.3 Query Management Tools

The Query Management Tools facilitate service discovery and service selection based

on service capability descriptions and service identiVcation. As mentioned bef...

... middle of paper ...

...ldType is introduced to add support for addressing individual nodes20

in a RDF graph. The only child element of a SemanticFieldType is the Var element which

either contains a descriptive identiVer starting with an exclamation mark similar to

SPARQL syntax or a speciVc URI. A SemanticFieldType is used in sorting and comparison

expressions.

The PreVx element adds a convenient way to deVne one or more preVxes for XML

namespaces which signiVcantly reduces the size of the query if a lot of Uniform Resource

IdentiVers are used. These preVxes can then be utilized within the QueryCondition and

OutputDescription elements.

To deVne the desired structure and substance of the result set of a semantic MPQF query

the OutputDescription element is enhanced by the addition of one or more ReqSemantic-

Fields. This element must contain a descriptive identiVer similar to Var.
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