Nothing Essay

344 WordsApr 9, 20142 Pages
Structuring System Data Requirem ents i In trod u ction ... In Chapter 7, you learned how to model and analyze two im portant views of an information system: (1) the flow o f d ata betw een m anual o r au to m ated steps and (2) the decision logic o f processing data. None of the techniques discussed so far, however, has con centrated on the data that m ust be retained in order to support the data flows and processing described. For example, you learned how to show data stores, or data at rest, in a data flow diagram (DFD). The natural structure of data, however, was n o t shown. DFDs, use cases, and various processing logic techniques show how, where, and when data are used or changed in an inform ation system, but these techniques do not show the definition, structure, and relationships w ithin the data. Data m odeling develops these missing, and cru cial, pieces of description of a system. In fact, some systems developers believe that a data m odel is the m ost im p o rtan t p art of the state m e n t o f in fo rm a tio n system re q u irem e n ts. T his b elief is based on the following reasons. First, the 2 8 2 Learning Objectives After studying this chapter, you should be able to: ■ Concisely define each of the following key data modeling terms: entity type, attribute, multivalued attribute, relationship, degree, cardinality, business rule, associative entity, trigger, supertype, subtype. ■ Draw an entity-relationship (E-R) diagram to represent common business situations. ■ Explain the role of conceptual data modeling in the overall analysis and design of an information system. ■ Explain the role of prepackaged database models (patterns) in data modeling. ■ Distinguish among unary, binary, and ternary relationships and give an example of each. ■ Define four basic types of business rules in a conceptual data

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