IMS TIERS Thomas D. Wason, Ph.D. University of North Carolina at Chapel Hill

Summary TIERS: TIEred Repository System. TIERS is a system for managing metadata schemas and vocabularies through multiple repositories.

TIERS and IMS TIERS was started at Carolina under the Instructional Management Systems (IMS) project of Educom ( NIST is currently implementing the first repository. TIERS was originally intended for educational resources, but it was soon recognized that educational resources have much in common with many other resources.

Architecture A metadata schema repository provides information about metadata schemes and dictionaries. It accessed through an interface to provide schema information for tagging and searching.

Balance A system of metadata must have a balance of prescriptive and the generative specifications. –A prescriptive specification tightly defines things. –A generative specification permits the creation and change of things.

Five basic needs related to accessing resources using metadata: Three are prescriptive: 1. Metadata is applied using a scheme that PRESCRIBES how things will be labeled. 2. In order to find things, you have to access the metadata schemes. 3. Prescriptive schemes must have stability and persistence so that the searcher and cataloger are effectively communicating.

Five basic needs related to accessing information using metadata: Two are generative: 4. Different groups (or disciplines) have different labeling needs. 5. Labeling needs change.

Prescriptive Needs #'s 1, 2 and 3 clearly state a requirement for well defined, stable metadata systems. These are prescriptive systems that define: –Schemes (e.g., fields and subfields) –Vocabularies (e.g., taxonomies and ontologies) 1. Metadata is applied using a scheme that PRESCRIBES how things will be labeled. 2. In order to find things, you have to access the metadata schemes. 3. Prescriptive schemes must have stability and persistence so that the searcher and cataloger are effectively communicating.

Generative Needs #'s 4 and 5 state a requirement for variation across disciplines and change over time. A generative system supports variability. 4. Different groups (or disciplines) have different labeling needs. 5. Labeling needs change.

Apparent Conflict Prescriptive and generative specifications are opposites. These two needs would seem to reflect a conflict of: Stability and Change. Stability and change are characteristics of evolution!

Evolution Evolution manages the balance between change and stability through selection. TIERS is conceived with the principles of evolution in mind.

A Hierarchy of Repositories TIERS is a hierarchy of repositories. TIERS follows an Object Oriented Design (OOD). Each repository is an object. Objects have methods, properties, and interfaces. Objects are well encapsulated.

Multiple Repositories Multiple repositories are structured in an OOD.

A TIERS Repository A TIERS repository contains four elements: 1. Dictionary 2. Type Library 3. Member List 4. Rules

Dictionary Contains attributes of elements per ISO Attributes of elements: Name Definition Scope Datatype Permitted values Comments

Dictionary Vocabularies Permitted values may include vocabularies A repository may contain discipline specific vocabularies in its dictionary. A vocabulary my contain keywords and a taxonomy.

Dictionary A dictionary provides a stable set of elements from which defined schemes can be created. A schema is a set of fields and subelements. A schema is a structure.

Type Library Resource objects are called “containers”. The type library contains “container” definitions.

Type Library A container type defines a field set and the obligations of each of the fields and subelements.

Type Library The container types in the library are organized as an object library.

List of Members Each (parent) repository can have members, which are listed. If the rules of the parent repository permit it, a member may have a repository that is a child of the parent repository.

Registration A repository’s type library, dictionaries, and vocabularies can be extended. Extensions can be registered. Registration is accomplished via the repository’s member list.

Multiple Repositories Multiple repositories are structured in an OOD via the list of members.

Rules The rules are what provide the methods and interfaces to the repository objects. The internal rules govern the methods within the repository. There are external rules that govern exchanges between repositories.

Rules Rules are organized into four categories: –Dictionary Rules –Container Type Sheet Rules –Rule Rules –Relationship Rules

Dictionary Rules A repository can inherit any dictionary elements from its parent. –It does not need to inherit all dictionary elements from its parent [a selective process].

Dictionary Rules A repository must have dictionary elements for each of the elements used in its useable container type sheets.

Dictionary Rules Corollaries: –A repository must inherit all dictionary elements listed in the type sheets it inherits. –A useable type sheet can only use elements that are contained in its host repository's dictionary(ies). NOTE: Dictionaries may contain both inherited and local elements, consequently, a container type sheet may contain both inherited and local elements.

Dictionary Rules A repository may define the maximum allowable dictionary size for itself and all of its descendants [a selective process].

Dictionary Rules A repository may submit a dictionary element to its parent repository for inclusion in a parent repository's dictionary. A repository does not have to accept a dictionary element submitted to it [a selective process].

A repository must have a defined method for editing its dictionaries. This will probably involve participation by the repository members. It may involve negotiations among members [a selective process]. Negotiations among people is a significant part of TIERS. These negotiations are encapsulated in the repository objects. Dictionary Rules

Container Type Sheet Rules A repository does not have to contain any type sheets, but inherit them by reference. A repository can inherit object type sheets only from its parent (multiple inheritances are not now enabled). The owner of a repository can elect to derive object type sheets from its parent's library of object type sheets (e.g., the parent's core elements plus possible additions). Type sheets in a repository must be descended (derived directly or indirectly) from type sheets in its parent repository. An object type sheet can be derived from a parent repository's type sheet library only by the owner of a repository. Object type sheets know which object type sheets are their children both within and outside of a repository.

Container Type Sheet Rules (cont.) The object type sheet library has two categories of type sheets: those that are available for use through the library, and those that are contained for inspection only. The inspectable type sheets serve to enhance the discovery process. A host repository may report to its parent repository only those object type sheets in the host library whose elements are contained in that host library's dictionary. In other words, a repository may contain object type sheets for which it does not have all of the elements in its dictionary, but those elements are contained in a dictionary in a child repository. Such incomplete definitions can only exist for one level. Object type sheets that do not have completely defined elements in a repository's dictionaries are only inspectable. They cannot be used through that repository.

Container Type Sheet Rules (cont.) Reported object type sheets retain the information of which repository reported it for n levels. n is subject to the rules of the system. The default of n is one (1). A repository will retain the inheritance relationships of object type sheets reported to it. A user of a repository may create new container types sheets within the rule system of that repository. Not all repositories may elect to allow this privilege (internal rule).

Rule Rules A repository inherits rules from its parent. A repository can determine which rules must be inherited by its children (forced inheritance). Not all rules in a repository must be inherited. A repository may create new rules if they do not conflict with existing forced inherited rules. If a forced inherited rule changes, that change is passed down to child repositories. Rules inherited from a parent cannot be made less restrictive by the child.

Relationship Rules A repository has only one parent (currently no multiple inheritance). A repository "knows" who its parents and children are. A repository is not required to accept an application for membership. In this way, a repository may have rules for repository stewardship that it can require be met. This will serve the ISO 9000 standard for quality control. A repository may give access to its members list for purposes of TIERS navigation. It is not required to give access.

TIERS Summary TIEred Repository System

A TIERS Repository

Multiple Repositories Multiple repositories are structured in an OOD via the list of members.

Metadata Use and Interchange A key to metadata creation, use and interchange is knowledge about the metadata. This is meta-meta-data. TIERS manages and provides meta-meta-data.

Architecture A metadata schema repository provides information about metadata schemes and dictionaries (with vocabularies).

IMS TIERS Tom Wason