This chapter describes the Graph Data Model (GDM) that underlies the GDL Data Definition and Data Manipulation Languages. A schema is represented by a labeled directed graph whose nodes represent records and whose arcs represent links. A query is formulated as an algebraic expression on the graph. Our data language to express queries is called an Elementary Data Language. The operations on the graph are called Elementary Data Operations, and these include manipulations of both records and links. The semantics of links are incorporated into the data model as definitions of link operators. Relationships among records are represented directly by the properties of linkage. It will be shown that a link-based data language is at least as powerful as a value-based data language.
KeywordsTerminal Node Relational Algebra Link Operator Link Type Record Type
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