OSID Specifications
type package
Version 3.0.0
Release Candidate Preview
TitleType Open Service Interface Definitions

The Type OSID defines a set of interfaces for managing Type definitions. Types are used as an identifier primarily for identification of interface extensions throughout the OSIDs and occasionally used as an extensible enumeration. An agreement between an OSID Consumer and an OSID Provider means they support the same Type.


A Type is similar to an Id but includes other data for display and organization. The identification portion of the Type is globally unique and contains:

  • authority: the name of the entity or organization responsible for the type. Using a domain name is a reasonable convention.
  • identifier: a string serving as an id. The identifier may be a urn, guid, oid or some other means of identification. Since all of the identification elements including the domain and authority create an overall unique Type, the identifier may even be a sequence number defined within a particular domain.
  • namespace: a string identifying the namespace of the identifier, such as "urn" or "oid".


                         Type type = lookupSession.getType("asset", "uri",         
                         print type.getDisplayName();

The sessions in this OSID offer the capabilities of a Type registry to centrally manage definitions and localized display strings and descriptions. Applications may opt to construct their own Types directly and bypass this service.

Type Hierarchies

Types are part of an internal hierarchy. A Type in a hierarchy includes the Types of its children. For example, an Asset may have a "photograph" Type included as part of an "image" base Type.

Unless an application will display a type, it can simply construct a type based on the identification components. OSID Providers may benefit by using this service to manage the type hierarchy, to provide a place to perform mappings across different type definitions, and to provide displayable metadata to its consumers.

Type Type Relations

Types may relate to other Types to describe constraints or compositions. The relationship is expressed as another Type. For example, a Position of type "researcher" may be appropriately associated with an Organization of type "laboratory" using a relation Type of "allowed." Or, a root Event type depends on a root TimePeriod type using a relationship type of "depends on."

Types for Constraints and Side Effects

An OSID Provider may link a Type, such as a genus, to a set of constraints that are made known to the application as Metadata through an OsidForm. Types of an OsidObject may also be used by an OSID Provider to constrain the possible relationship Types that may be possible to that OsidObject. In these uses of Types, there is a semantic accompanying the Type definition managed within an OSID Provider. The Type OSID manages the metadata of the Type itself. Logic implementing the meaning of the Type is managed completely within an OSID Provider.

OSIDs emphasize relationships over data typing since type agreements are often an impediment to interoperability. Generally, the rule of thumb for record Types is to first explore other OsidObjects, even those in other OSIDs for a place for extra data. Often, what is hiding behind a list of data elements is a separate service that can be provided as a separate module and serves to keep the principal OsidObject lighter and more flexible.

Genus Types primarily serve as a quick and dirty way to unclutter the record Types with "is kind of like" tags. OsidCatalogs can be used for a richer solution. For example, a genus Type may be used to identify all Events on a Calendar which are classes at a school and is accompanied by constraint logic such that the Events occur at a Location on campus.

Another pathway to explore is to create a smart Calendar from an EventQuery that specifies constrraints on the Event sponsor, Location, or other data required for classes. Creates and updates for Events in that smart Calendar will be similarly constrained and surfaced to the OSID Consumer through the Metadata in the EventForms. While this path is certainly more difficult than simply nailing up some logic indexed by a genus Type, it can be considered if there is a need to expose the logic and authoring capabilities.


Most OSID interfaces are used to encapsulate implementation-specific objects from provider to consumer. Type is an OsidPrimitive and as such cannot be used to encapsulate implementation-specific data other than what is defined explicitly in the Type. An OSID Provider must respect any Type constructed by an OSID Consumer.