Delivery Context modules
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Contents |
Introduction and current status
The Delivery Context Ontology [1] provides a formal model for the information of the environment in which devices interact with the Web or other services that can be used to adapt contents on a wide range of devices with different capabilities. The delivery context includes the characteristics of the device, the software used to access the service and the network providing the connection among others.
The current status of the Delivery Context Ontology (date: April of 2008) has the following problems of maintenance
- Detecting inconsistencies. Currently the Delivery Context Ontology has a problem of consistency. There is a contradiction within the axioms of the TBox of the ontology, but it is very difficult to detect where is this contradiction due to the complexity of the relational model and mainly due to its big size. We have run Pellet reasoner to check ontology's consistency and it returns the following:
DL Expressivity: ALCHOF(D) Consistent: No Reason: Individual http://www.w3.org/2007/uwa/ontologies/DeliveryContext.owl#ExampleDC_1 is forced to belong to class http://www.w3.org/2007/uwa/ontologies/DeliveryContext.owl#Environment and its complement
Certainly it is not critical for the purposes of the MyMobileWeb project wether the Delivery Context Ontology is a not logically consistent model, as the objective of the model is only to provide a common vocabulary to describe the capabilities of devices and other relevant resources for content-adaptation. Nevertheless, it is a desirable objective from the knowledge representation perspective to build a formal model compliment with design expectations of the OWL language usage, as a first-order logical language. Moreover, a contradiction in the logical model of the ontology disables us to use the description logics deductive rules associated with OWL (e.g. inference rules for subsumption).
Delivery Context Refactorization
- Semantic isolation. The concepts and properties of the Delivery Context Ontology have been exclusively designed for their use in this project with any explicit reference to other specific, domain ontologies available in the web that have adressed before some of the modelling challenges of MyMobileWeb. For instance, the properties to express geographical location of resources in the Delivery Context Ontology are longitude and latitude, instead of using properties from well-known vocabularies such as the Basic Geo (WGS84) Vocabulary [2], a basic RDF vocabulary that provides the Semantic Web community with a namespace for representing latitude:geo:lat and longitude: geo:long using WGS84 as a reference datum. This situation makes difficult to relate the Delivery Context Ontology with other external efforts outside the MyMobileWeb Project and force us to maintain our own ontologies ior semantic descriptions for every relevant element of the Delivery Context.
These problems should be adressed to obtain an useful, shared formal model in the context of the MyMobileWeb project.
Proposal
This section describes how to refine the design of the Delivery Context. The proposal consists in spliting up the current ontology into a set of down-size ontologies. Therefore, the complete model of the Delivery Context will be distributed along several semantically interlinked modules. DC modules will be used to extend the available terms of a core and central module, and also to avoid making the DC Ontology too complex and unreadable. We suggest the following division:
- A core ontology for the DC formalization. This ontology is the common framework which provides the main important concepts and properties for the description of the delivery context in the MyMobileWeb Platform. Basically, this core module identifies the semantic skeleton of the DC (device, user, network, environment, etc.) and a set of properties to express relationships between. The DC core ontology specially emphasizes the formal description of profiles: UserProfile, NetworkProfile and UserProfile. A remark has to be highlighted about the new structure of the DC ontology. The instances of these concepts should be defined with the elements of the DC modules or other RDF vocabularies. The Core DC ontology only gives the basic properties, which should be refined or extended outside this minimal model.
- Set of semantic modules. Each one will be an specific ontology based on the already existing Delivery Context Ontology. In addition, the content of these ontologies will be extracted from the current design of the Delivery Context ontology: branchs in the hierarchy of classes under the Delivery_Context_Entity concept will be isolated as single ontologies. Obviously, more effort is needed to refine the set of properties and classes and how they will be interlinked in the new scenario. The set of modules will be the following:
- Ontology for the description of the Location
- Ontology for the description of the Network
- Ontology for the description of the Device
- Ontology for the description of the User
- Ontology for the description of the Units of measurement
Namespaces and URIs for the Delivery Context modules
The core DC ontology is identified by the namespace http://www.w3.org/2007/uwa/ontologies/DeliveryContext/core/
The namespaces for the DC modules are build concatenating the basic DC URI pattern http://www.w3.org/2007/uwa/ontologies/DeliveryContext/ with the name of the module, e.g. the ontology's namespace for the description of devices is http://www.w3.org/2007/uwa/ontologies/DeliveryContext/devices/.
A slash-namespace is used. This makes it possible for semantic web agents to retrieve the definitions of each resource individually, i.e., avoiding the burden of retrieving the definition of all the resources stored in the RDF model when the application is interested in just one of them. More information to publish this set of ontologies can be found in the Recipes document from the W3C [3].
New design decissions for the set of DC ontologies
New design decisions have to be taken to adpat the already formalized knowledge:
- Select the appropriate fragment of OWL. As it is mentioned above, the purpose of the DC ontology is to provide a common,shared vocabulary to formally describe DC entities, but we do not foresee at the current stage of the project a practical use of DL reasoners (classification or realization operations) for content-adaptation. On the contrary, our concern is mainly how to efficiently scale the knowledge base from a computational (rather than formal) view, and how the infomation stored in the DC model will be consume by the MyMobileWeb Platform for content-adaptation and for context-based suggestions, or by other third-party applications. We suggest to keep the logical expressivity of the DC ontology in the RDF03 fragment [4], a strict subset of OWL.
- Refine the subclass tree and the subproperties tree. The process of re-engineering the DC ontology can be simplified if we use an upper-level ontology. These kind of generic ontologies provide clues and specific methodologies to interpret entities of a particular domain (as it is the Delivery Context domain). This approach has been taken, for instance, to represent qualities of devices (such weight, width, etc.)and their relationships to units and measurement values with a strong ontological commitment