Content Management
While other infrastructures for the manipulation of content in Grid-based environments, like gLite, provide basic file-system like functionality for content manipulation, the Information Organization services are aimed to provide more high-level functionality, built on top of gLite or other storage facilities. Content is stored and organized following a graph-based data model, the Information Object Model, that allows finer control of content w.r.t. a file based view, by incorporating the possibility to annotate content with arbitrary properties and to relate different content unities via arbitrary relationships. Building on this basic data model, other services in the Information Organization family provide to other gCube services more sophisticated data models to manage complex documents, document collections, metadata and annotations.
Information Object Model The elementary constructs of the model are information-objects (a node of the graph) and object references (the arcs). The ER Diagram in Figure 20 describes the model. An Information Object (IO) represents an elementary information unity. It is uniquely identified by an Object Identifier (OID), is labelled with a name1 and a type2 and Information optionally annotated with a number of properties. These properties are simple key-type-value associations. Finally, it can be associated with a raw-content. The raw content of an object is content of any kind. The model hides the actual storage details of the content of an object, that can be for instance stored as a file in gLite or as BLOB-field in a database, or maintained in storage facilities not under direct control of the Information Organization Services, e.g. as file stored in a remote server and accessible through some protocol like http, ftp or gridftp. An object reference “links” two Information Objects. Each object might (i) reference many other objects and (ii) be referenced by many objects (m-n relationship). A reference is directed, it is labelled with a type attribute, called primary role, a secondary role, that may optionally further specify the function of the primary role3, and a position attribute, that allows to build ordered graph structures. It can also be associate with a number of other properties. The information-object model introduced above is exposed to higher level Information Organization Services by a component called the Storage Management Service (cf. Section 6.3). The generality of this simple information model allows to build complex data-structures. The services within the Information Organization stack build on top of this model to offer an organized, high-level view of content. This is done by attaching specialised semantics to the labels used to annotate Information Objects and references.
