SummaryΒΆ
Type Open Service Interface Definitions type version 3.0.0
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
.
Types
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”.
- Example
- Type type = lookupSession.getType(“asset”, “uri”,
- “http://harvestroad.com/osidTypes/image”, “harvestroad.com”);
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.
OsidPrimitives
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.