All resources define a capability named osgi.identity that determines their
Resources provide a set of Capability objects describing the features they
Resources provide a set of Requirement objects describing the features they
need to run.
Resources use the osgi.identity and the optional osgi.content capabilities
to provide a set of named attributes describing the resource.
Despite the vague nature of Resource objects, these
rules mean that they aren't as complicated as you
might think. In figure 7.1, you can see that a Resource
is not much more than a holder for Requirement and
Every resource exposes three mandatory attributes
through the osgi.identity capability:
■ type —The type of the resource
■ osgi.identity —The symbolic name or iden-
tity of the resource
■ version —The version of the resource
Other attributes, such as the license, description, and
links to documentation, may also be included. Further
predefined attributes that broadly correspond to
other informational headers in the bundle manifest
file are defined by the osgi.wiring.bundle , osgi.wiring.package , and osgi.wiring
.host capabilities. Any of a resource's capabilities may also contain arbitrary keys and
values that are used in a resource type-specific way.
Figure 7.1 Resources may have
requirements and capabilities.
IDENTITY OF RESOURCES
The identity of a resource is, unsurprisingly, defined by the attributes of the
osgi.identity capability. For a particular type of resource, the combination of
osgi.identity and version attributes provides a unique identifier, but it's impor-
tant to remember that, when comparing resources, they may not be of the
same type. This is why it's always important to refer to the whole osgi.identity
capability. With the cornucopia of potential resource types, OSG i defines a standard
type for OSG i bundles ( osgi.bundle ) and fragments ( osgi.fragment ). Any OSG i
bundle modeled as a resource will have an identity type of osgi.bundle and an
osgi.identity corresponding to its symbolic name, instantly separating it from the
crowd of configuration property and steamed pudding resources in the repository,
even if one of those puddings has exactly the same name and version as your bun-
dle (see figure 7.2).
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