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1.1 Two Problems |
1.2 Concept of the Solution |
1.3 Composition- Diagrams |
1.4 Process- Diagrams |
1.5 Data- Structur- Diagrams |
1.6 Metadiagram of the FMC-Diagrams |
1.7 Layering of Interpreters |
1.8 Separation of Phases |
1.5 Data Structure Diagrams
A data structure diagram shows which component types occur in a data structure and how these component types are related to one another. For this purpose, the component types and the relationships are symbolized by two-dimensional nodes. The information about a certain component type being involved in a certain relationship is represented by a line whose one end lies on the boundary of the component type node and whose other end lies on the boundary of the relationship node. Component type nodes differ from relationship nodes by the shape of their boundaries. Relatioship nodes always have the shape of rectangles, whereas for the shapes of the boundaries of component type nodes, the same rules apply as for the action field nodes in composition diagrams: In the simplest case, a component type node has the shape of a circle. However, it may also contain horizontal and vertical straight sections connected by half or quarter circles.In computer science it is common to use the term entity instead of component type, and the diagrams are called entity relationship diagrams (ERDs).
The data structure diagram above is given as an example. It is about the data in a software system that could be used in travel agencies.
The following information can be found in this data structure diagram:
- A part of the data contains the information which flights can be booked,
including the specification of these flights such as
their destinations, which airline offers the respective flight, and the dates of departure and arrival.
- The data also includes information which bonus programs the airlines offer.
- Another component of the data is the information about the persons who are the travel agency's customers,
the flights they have booked, and whether and how they referred to which bonus program.
It is a fundamental feature of the data structure diagrams that the interpretation of the component types are characterized by nouns - flight, airport, airline, customer, bonus program - whereas the relationships are characterized by verbs - arrives, departs, is offered , offers, has booked.