Information Technology Reference
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equivalent to the notion of any information realization in the large, while our use of
the term is instead for representations sent over the Web using HTTP. Furthermore,
one can distinguish
web resources
(
WebResource
) as a subset of information
resources that are
under normal conditions
usually web-accessible, i.e. the server is
not down, the browser works normally, etc.
In terms of HTTP, a
WebRepresentation
is an entity (associated with
various entity headers and an entity body) that is also subject to content negotiation
and so may be transferred as multiple entities. This is because, as given in IETF
RFC 2616, a Web representation may be defined as “an entity included with a
response that is subject to content negotiation” such that “there may exist multiple
representations associated with a particular response status” (Fielding et al. 1999).
Therefore, we define
WebRepresentation
as a sub-class of a more general
Entity
class as defined by HTTP RFC 2616 (Fielding et al. 1999). The term
'entity' could be confusing as it is often used in many other philosophical and
technical contexts. However, in HTTP an
entity
may be the information given
by either an HTTP request or response, but a Web representation, by virtue of
being a 'representation' of a resource, is only for an HTTP response. A web
representation is thus a kind of entity that is about the state of a resource as defined in
AWWW (Jacobs and Walsh 2004), but there are entities that only request the state
of resources or indicate that requests can or cannot be fulfilled. For example, an
HTTP POST request or even a 404 response are entities but they do not necessarily
represent the state of a particular web resource. An entity may be transferred as the
request or response of many particular actions by a client. For example, different
URIs may return the same entity, such as when one URI hosts a copy of a resource
given by another URI. In order to model the complexity of headers and bodies in
HTTP entities, we use another popular content ontology pattern, the
Composition
pattern, referred to as
comp:
. This pattern, extracted from the DOLCE Ultra
Lite ontology,
11
allows us to model a non-transitive component-whole relationship,
which however implies (by subsumption) a transitive part-of relation.
http:Entity
: An OWL Class. “The information transferred as the payload of
a request or response” (Fielding et al. 1999). “An entity consists of metainforma-
tion in the form of entity-header fields and content in the form of an entity-body”
(Fielding et al. 1999).
-
rdfs:subClassOf ir:InformationRealization
-
comp:hasComponent exactly 1 http:EntityHeader
-
comp:hasComponent max 1 http:EntityBody
http:EntityBody
: An OWL Class. Whatever information is sent in the
request or response is in “a format and encoding defined by the entity-header
fields” (Fielding et al. 1999). Also called in HTTP the 'content' of a message
(Fielding et al. 1999).
-
http:hasMediaType
o
http:MediaType
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