TAILIEUCHUNG - Lecture Enterprise systems development - Lecture 27

In this chapter, students will be able to: Describe how a service-oriented architecture can be used as a philosophical approach to help the organization of the future meet all its IT-related needs, define and describe the various hardware and software infrastructure considerations in an organization. | Lecture 27 Enterprise Systems Development ( CSC447) COMSATS Islamabad Muhammad Usman, Assistant Professor College of Statistical and Acturial Science E-R Design Decisions The use of an attribute or entity set to represent an object. Whether a real-world concept is best expressed by an entity set or a relationship set. The use of a ternary relationship versus a pair of binary relationships. The use of a strong or weak entity set. The use of specialization/generalization – contributes to modularity in the design. The use of aggregation – can treat the aggregate entity set as a single unit without concern for the details of its internal structure. E-R Diagram for a Banking Enterprise Summary of Symbols Used in E-R Notation Summary of Symbols (Cont.) Reduction to Relation Schemas Primary keys allow entity sets and relationship sets to be expressed uniformly as relation schemas that represent the contents of the database. A database which conforms to an E-R diagram can be represented by a collection of schemas. For each entity set and relationship set there is a unique schema that is assigned the name of the corresponding entity set or relationship set. Each schema has a number of columns (generally corresponding to attributes), which have unique names. Representing Entity Sets as Schemas A strong entity set reduces to a schema with the same attributes. A weak entity set becomes a table that includes a column for the primary key of the identifying strong entity set payment = ( loan_number, payment_number, payment_date, payment_amount ) Representing Relationship Sets as Schemas A many-to-many relationship set is represented as a schema with attributes for the primary keys of the two participating entity sets, and any descriptive attributes of the relationship set. Example: schema for relationship set borrower borrower = (customer_id, loan_number ) Redundancy of Schemas Many-to-one and one-to-many relationship sets that are total on the many-side can be represented

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