Knowledge graph

djehuty processes its information using the Resource Description Framework (Lassila, 1999). This chapter describes the parts that make up the data model of djehuty.

3.1 Use of vocabularies

Throughout this chapter, abbreviated references to ontologies are used. Table 3.1 lists these abbreviations.

Table 3.1: Lookup table for vocabulary URIs and their abbreviations.

3.2 Notational shortcuts

In addition to abbreviating ontologies with their prefix we use another notational shortcut. To effectively communicate the structure of the RDF graph used by djehuty we introduce a couple of shorthand notations.

3.2.1 Notation for typed triples

When the object in a triple is typed, we introduce the shorthand to only show the type, rather than the actual value of the object. Figure 3.1 displays this for URIs, and figure 3.2 displays this for literals.

Figure 3.1: Shorthand notation for triples with an rdf:type which features a hollow predicate arrow and a colored type specifier with rounded corners.

Literals are depicted by rectangles (with sharp edges) in contrast to URIs which are depicted as rectangles with rounded edges.

Figure 3.2: Shorthand notation for triples with a literal, which features a hollow predicate arrow and a colored rectangular type specifier.

When the subject of a triple is the shorthand type, assume the subject is not the type itself but the subject which has that type.

3.2.2 Notation for rdf:List

To preserve the order in which lists were formed, the data model makes use of rdf:List with numeric indexes. This pattern will be abbreviated in the remainder of the figures as displayed in figure 3.3.

Figure 3.3: Shorthand notation for rdf:List with numeric indexes, which features a hollow double-arrow. Lists have arbitrary lengths, and the numeric indexes use 1-based indexing.

The hollow double-arrow depicts the use of an rdf:List with numeric indexes.

3.3 Datasets

Datasets play a central role in the repository system because every other type links in one way or another to it. The user submits files along with data about those bytes as a single record which we call a djht:Dataset. Figure 3.4 shows how the remainder of types in this chapter relate to a djht:Dataset.

Figure 3.4: The RDF pattern for a djht:Dataset. For a full overview of djht:Dataset properties, use the exploratory from the administration panel.

Datasets are versioned records. The data and metadata between versions can differ, except all versions of a dataset share an identifier. We use djht:DatasetContainer to describe the version-unspecific properties of a set of versioned datasets.

Figure 3.5: The RDF pattern for a djht:DatasetContainer. All versions of a dataset share a djht:dataset_id and a UUID in the container URI.

The data model follows a natural expression of published versions as a linked list. Figure 3.5 further reveals that the view, download, share and citation counts are stored in a version-unspecific way.

3.4 Accounts

djehuty uses an external identity provider, but stores an e-mail address, full name, and preferences for categories.

Figure 3.6: The RDF pattern for an djht:Account.

3.5 Funding

When the djht:Dataset originated out of a funded project, the funders can be listed using djht:Funding. Figure 3.7 displays the details for this structure.

Figure 3.7: The RDF pattern for a djht:Funding.