Graph Database for Collaborative Communities - Community-Built Databases: Research and Development - page 213

Fig. 9.7 GOOD queries

Fig. 9.8 Object Exchange Model (OEM). Schema and instance are mixed

Lorel

Lorel [ 18 ] is implemented as the query language of the Lore prototype database
management system at Stanford ( http://www.db.stanford.edu/lore ).
It is used for the Object Exchange Model (OEM) data model (Fig. 9.8 ). A
database conforming to OEM can be thought of as a graph where Object-IDs
represent node labels and OEM labels represent edge labels. Atomic objects are
leaf nodes where the OEM value is the node value. Lorel allows flexible path
expressions, which allow querying without precise knowledge of the structure. Path
expressions are built from labels and wildcards (placeholders) using regular expres-
sions, allowing the user to specify rich patterns that are matched to actual paths
in the graph database. Lorel also includes a declarative update language.

GraphDB

G uting [ 20 ] proposes an explicit model named GraphDB, which allows simple

modeling of graphs in an object-oriented environment. A database in GraphDB is a
collection of object classes where objects are composed of identity and tuple
structure; attributes may be data- or object-valued. There are three different kinds
of object classes called simple classes, link classes, and path classes. Simple objects
are just objects, but also play the role of nodes in the database graph. Link objects
are objects with additional distinguished references to source and target simple

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