Lesson 3.7 Systems Analysis Flashcards
Concisely define each of the following key data-modeling terms: conceptual data model، entity-relationship diagram، entity type، entity instance، attribute، candidate key، multivalued attribute، relationship، degree، cardinality، and associative entity.
A conceptual data model represents the overall structure of organizational data، independent of any database technology. An E-R diagram is a detailed representation of the entities، associations، and attributes for an organization or business area. An entity type is a collection of entities that share common properties or characteristics. An attribute is a named property or characteristic of an entity. One or a combination of attributes that uniquely identifies each instance of an entity type is called a candidate key. A multivalued attribute may take on more than one value for an entity instance. A relationship is an association between the instances of one or more entity types، and the number of entity types participating in a relationship is the degree of the relationship. Cardinality is the number of instances of entity B that can (or must) be associated with each instance of entity A. Data that are simultaneously associated with several entity instances are stored in an associative entity.
Ask the right kinds of questions to determine data requirements for an information system
Information is gathered for conceptual data modeling as part of each phase of the systems development life cycle. You must ask questions in business، rather than data modeling، terms so that business managers can explain the nature of the business; the systems analyst represents the objects and events of the business through a data model. Questions include: What are the objects of the business? What uniquely characterizes each object? What characteristics describe each object? How are data used? What history of data must be retained? What events occur that relate different kinds of data، and are there special datahandling procedures?
Draw an entity-relationship (E-R) diagram to represent common business situations.
An E-R diagram uses symbols for entity، relationship، identifier، attribute، multivalued attribute، and associative entity and shows the degree and cardinality of relationships (see Figure 7-5 for all the symbols and see Figures 7-3 and 7-11 for example diagrams). Exercises at the end of the chapter give you practice at drawing E-R diagrams.
Explain the role of conceptual data modeling in the overall analysis and design of an information system.
Conceptual data modeling occurs in parallel with other requirements analysis and structuring steps during systems development. Information for conceptual data modeling is collected during interviews، from questionnaires، and in JAD sessions. Conceptual data models may be developed for a new information system and for the system it is replacing، as well as for the whole database for current and new systems. A conceptual data model is useful input to subsequent data-oriented steps in the analysis، design، and implementation phases of systems development where logical data models، physical file designs، and database file coding are done.
Distinguish between unary، binary، and ternary relationships، and give an example of each.
A unary relationship is between instances of the same entity type (e.g.، Is_married_to relates different instances of a PERSON entity type). A binary relationship is between instances of two entity types (e.g.، Registers_for relates instances of STUDENT and COURSE entity types). A ternary relationship is a simultaneous association among instances of three entity types (e.g.، Supplies relates instances of PART، VENDOR، and WAREHOUSE entity types)
Distinguish between a relationship and an associative entity، and use associative entities in a data model when appropriate.
Sometimes many-to-many and one-to-one relationships have associated attributes. When this occurs، it is best to change the relationship into an associative entity. For example، if we needed to know the date an employee completed a course، Date_Completed is neither an attribute of EMPLOYEE nor COURSE but of the relationship between these entities. In this case، we would create a CERTIFICATE associative entity (see Figure 7-7)، associate Date_Completed with CERTIFICATE، and draw mandatory one relationships from CERTIFICATE to each of EMPLOYEE and COURSE. An associative entity، like any entity، then may be related to other entities.
Relate data modeling to process and logic modeling as different ways of describing an information system
Process and logic modeling represent the movement and use of data، whereas data modeling represents the meaning and structure of data. A data model is usually a more permanent representation of the data requirements of an organization than are models of data flow and use. Still، consistency between these models of different views of an information system is required. For example، all the data in an E-R diagram for an information system must be in data stores on associated data-flow diagrams.
Generate at least three alternative design strategies for an information system.
Generating different alternatives is something you would do in actual systems analysis or as part of a class project. Three is not a magic number. It represents instead the endpoints and midpoint of a series of alternatives، such as the most expensive، the least expensive، and an alternative somewhere in the middle.
Select the best design strategy using both qualitative and quantitative methods.
Once developed، alternatives can be compared to each other through quantitative methods، but the actual decision may depend on other criteria، such as organizational politics. Here، you were introduced to one way to compare alternative design strategies quantitatively.
How many separate entity-relationship diagrams can conceptual data modeling produce?
Four
A single occurrence of an entity type is known as a(n) ___.
Entity instance
True or False? A relationship can be modeled as an entity type in an E-R diagram.
.True
