6.4.3. Retrieval

This section describes the components and procedures for using Z39.50 to return records in response to a query. The CIMI Profile specifies a CIMI tagSet that identifies elements, a CIMI Schema, and an associated abstract record structure. The Profile also defines an Abstract Record Structure (ARS) for the retrieval record. The ARS specifies the use of elements from tagSet-M, tagSet-G, tagSet-Collections, and tagSet-CIMI.

The CIMI Profile is a companion profile to the Z39.50 Profile for Access to Digital Collections [7] (referred to as the Digital Collections Profile). The CIMI Profile uses the Digital Collections Schema's "descriptive object record" in a conformant manner. The CIMI Profile, Release 1.0, focuses on retrieval of resources rather than navigation among collections, and the ARS for the retrieval record specifies only those elements of the Digital Collections Schema that are pertinent to the goal of retrieval. CIMI Z-clients and Z-servers optionally may use, in a conformant manner, other Digital Collections Profile specifications. CIMI anticipates future releases of the CIMI Profile will include additional specifications from the Digital Collections Profile.

6.4.3.1. The Retrieval Record: An Overview

The CIMI Profile defines a retrieval record to support three levels of semantic interoperability by partitioning the record into three levels of elements. In order of occurrence in the record, the record contains: elements that a Z39.50 client may understand even if it does not recognize any specific schema (i.e., "generic level of semantic interoperability"); elements that a Z39.50 client may understand if it recognizes the Digital Collections Schema but not the CIMI Schema (i.e., "Digital Collections level of semantic interoperability"); elements understandable to a Z39.50 client that recognizes the CIMI Schema (i.e., "CIMI level of semantic interoperability"). This partitioning allows for wider semantic interoperability between CIMI Z-servers and non–CIMI Z39.50 clients while enabling meaningful semantic interoperability for CIMI Z-clients.

Thus the ARS for the retrieval record specifies:

1. At the beginning of a retrieval record there may occur generic elements (in the form of tagSet–M and tagSet–G elements).
2. Following that, the Digital Collections Schema is assumed, and a Digital Collections–aware client can recognize and process these elements.
3. Following those elements, the CIMI Schema is assumed, and a CIMI Z-client can recognize and process the remaining elements in the record.

At the generic level of semantic interoperability, a generic Z39.50 client might search databases that include collection and object descriptive records as well as other types of records. By including generic elements at the top level of a retrieval record, such a client will be able to partially, if not fully, process these retrieval records.

At the Digital Collections level of semantic interoperability, a Z39.50 client aware of the Digital Collections Schema may perform a distributed search across multiple domains and over multiple collections including those provided by a CIMI Z-server. It may retrieve a record from the CIMI Z-server, and discover that there is a potential object of interest, even though the Z39.50 client is not able to fully process the record.

At the CIMI level of semantic interoperability, a Z39.50 client aware of the CIMI–specific Schema should be able to fully process a CIMI retrieval record.

To accommodate these levels of semantic interoperability, it is necessary to insert the element schemaIdentifier (tagSet-M element 1) at both interoperability boundary points within a retrieval record. The Digital Collections Schema identifier occurs when the record changes from the generic to the Digital Collections level, and the CIMI Schema identifier occurs when the record changes from Digital Collections level to the full CIMI level of semantic interoperability.

The term "abstract record structure" is commonly used within the context of a specific schema. For the CIMI Profile, the Abstract Record Structure for the Retrieval Record transcends the CIMI schema. Therefore, the CIMI Profile distinguishes:

• the CIMI Schema-specific abstract record structure (see Section 6.4.3.2.2.)
• the abstract record structure defining the complete retrieval record (see Section 6.4.3.3.).

6.4.3.1.1. Tag Types

At the generic level of semantic interoperability, the Abstract Record Structure for the Retrieval Record assumes the use of Tag Types 1, 2, and 3. At the Digital Collections level of semantic interoperability, the Abstract Record Structure for the Retrieval Record assumes the use of Tag Types 1, 2, 3, and 4. At the CIMI level of semantic interoperability, the Abstract Record Structure for the Retrieval Record assumes the use of Tag Types 1, 2, 3, 4, and 5.

6.4.3.1.2. The CIMI TagSet

This section defines the CIMI tagSet by identifying the tag value, element name, and ASN.1 datatype for each element. TagSet-CIMI is a registered object: OID = 1.2.840.10003.14.6.

6.4.3.2. The CIMI Schema

The CIMI Schema uses elements defined in tagSet–CIMI as well as tags from other registered tag sets. The CIMI Schema defines the constructed datatypes identified in the CIMI tagSet and describes an abstract record structure that provides the layout and ordering of elements. The CIMI Schema is a registered object: OID = 1.2.840.10003.13.5.

The Schema addresses the need to retrieve one or more "images" (where "images" can be any type of digital resource including audio, video, images) that may be available in one or more versions (e.g., differing resolutions, color-depth, and sampling rate). The element mrObject is a repeating element that occurs for each instance of an image, and each available version occurs in the repeating element rendition. Descriptive metadata may be provided for each instance of mrObject and for each instance of rendition (thus metadata and multiple renditions). Since information provided in the subelements for mrObject may apply to subelements in the element rendition (e.g., the value of the title subelement in mrObject is the same for that subelement in rendition), the subelements of rendition can assume by inheritance the values of the subelements from mrObject. Only in cases where a subelement in rendition takes on a value different from its parallel subelement in mrObject is there a need to include that subelement in the rendition element.

Within rendition, the subelement resource carries either a URL for the image or the actual bits that comprise the image. The subelement resource has information provided by appliedVariant (see Section 6.4.3.5.1 Use of GRS-1).

6.4.3.2.1. Constructed Datatypes

The CIMI Schema defines four constructed datatypes: CreatorInfo, MrObject, Rendition, MoreInfo. ASN.1 datatypes for tags from other tagSets (e.g., tagSet-G and tagSet-M) can be found in the definitions of those tagSets. See Z39.50 Maintenance Agency [17] http://lcweb.loc.gov/z3950/agency/defs/tag-gm.html for definitions of tagSet-G and tagSet-M.

Datatype CreatorInfo is structured as follows:

Datatype MrObject is structured as follows:

*The element date may be returned as either GeneralizedTime or EXTERNAL datatypes. See Z3950DateTime [16] http://lcweb.loc.gov/z3950/agency/defs/date.html for specifications when using EXTERNAL.

Datatype Rendition is structured as follows:

*The element date may be returned as either GeneralizedTime or EXTERNAL datatypes. See Z3950DateTime [16] http://lcweb.loc.gov/z3950/agency/defs/date.html for specifications when using EXTERNAL.

Datatype MoreInfo is structured as follows:

6.4.3.2.2. The CIMI Schema–Specific Abstract Record Structure

Associated with the CIMI Schema is a specific abstract record structure that identifies the ordering, tag values, and tag paths of the elements that are relevant only to the CIMI Schema. This Abstract Record Structure comprises the CIMI Schema–specific portion of the Abstract Record Structure for the Retrieval Record (see Section 6.4.3.3.).

* For each retrieval record, one of the following elements must be present:

(5,32) objectTitle (if the record is an object record or an image with text record)
(5,33) bibliographicTitle (if the record is a bibliographic record)

** If the element mrObject occurs, at least one occurrence of rendition and its subelement resource is mandatory.

6.4.3.3. The Abstract Record Structure for the Retrieval Record

The Abstract Record Structure for the Retrieval Record (below) addresses important goals of the CIMI Profile. First, it maintains alignment with the Digital Collections Profile in that it adopts a structure of that Profile’s Object Descriptive Record. The resources addressed by the CIMI Profile are modeled as digital objects. The CIMI Profile treats all content and descriptive information as digital objects, and to this extent does not exploit fully the functions of the Digital Collections Profile (e.g., for navigation of collections).

Second, the tagSet–G and tagSet-M elements at the beginning of the retrieval record allow semantic interoperability with Z39.50 clients that have no knowledge of either the Digital Collections Schema or the CIMI Schema. CIMI Z-servers will include, at the beginning of a retrieval record, the tagSet-G elements corresponding to the Dublin Core elements as listed below. Other tagSet–G and tagSet-M elements can occur at the beginning or elsewhere in the the record.

The Abstract Record Structure for the Retrieval Record uses the tagSet-M element schemaIdentifier to indicate interoperability boundary points as described in Section 6.4.3.1.

The following table provides usage guidance and/or required values for selected schema elements in the Abstract Record Structure.

The following Abstract Record Structure for the Retrieval Record describes the layout and order of the GRS record.

* For each retrieval record, one of the following elements must be present:

(5,32) objectTitle (if the record is an object record or an image with text record)
(5,33) bibliographicTitle (if the record is a bibliographic record)

** If the element mrObject occurs, at least one occurrence of rendition and its subelement resource is mandatory.

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