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- A node is an object or datastream.
- An edge is a relationship (in this case, a parent-child relationship) that links two nodes. Edges are represented as RDF properties in a Fedora object.
- A graph is a set of nodes connected by edges. The entire set of objects in the workspace and their relationships to each other form a graph.
- A directed graph is a graph whose edges have direction associated with them: that is, the relations that link the nodes move in a given direction from one node to the next. An example of an edge with a direction is isAChildOf. The relationship expresses a direction from the child to the parent. The relationship isParentOf can also link the same two nodes, but in the opposite direction.
- A directed acyclic graph is a graph where whose in which edges never form loops (i.e., cycles) of nodes. That is, if you start at node A, then follow a set of identical relations from that node to other nodes in a chain, you will never end up back at node A.
- A hierarchical tree, such as the one modeled in the Fedora repository workspace by the relationships provided by the JCR underpinnings of Fedora, is a classic example of a directed acyclic graph of nodes. In this sense, no Fedora object can ever be its own grandpa. Of course, the additional relationships that you, the user, distribute amongst your objects are entirely up to you. You can make them as simple or complex as you like.
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