Solutions_06

Solutions_06 - Systems Analysis and Design in a Changing...

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Systems Analysis and Design in a Changing World, Fourth Edition 6-1 Chapter 6 – The Traditional Approach to Requirements Solutions to End-of-Chapter Material Review Questions 1. List at least three different types of DFDs. What is each diagram type used to represent? Types of DFDs include context diagrams, event-partitioned system models, subsystem DFDs, diagram 0, DFD fragments, process decompositions, physical DFDs, and logical DFDs. A context diagram contains a single process representing the entire system. The diagram shows important interactions between the system and external agents. An event-partitioned system model contains one process per event. The model shows important interfaces with external agents. If no subsystem DFD is created, the event- partitioned system model is also called diagram 0. A subsystem DFD contains one process per major subsystem. The DFD shows important interfaces with external agents. Each process is further represented by another DFD—an event-partitioned DFD (or diagram zero) for that subsystem. A DFD fragment is a portion of an event-partitioned system model that shows the process, external agents, data stores, and data flows needed to respond to a single event. A process decomposition is a DFD that shows the internal implementation details of a single process on another DFD. A physical DFD is any DFD that shows the specifics of a particular system implementation. A logical DFD is any DFD that shows system requirements under the assumption of perfect technology. 2. List the five component parts (symbols) of a DFD. Briefly describe what each symbol represents. Process (a rectangle with rounded corners) – Represents an algorithm for transforming data input into data output. Data flow (a one- or two-headed arrow) – Represents the movement of data among processes, data stores, and external agents.
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Systems Analysis and Design in a Changing World, Fourth Edition 6-2 External agent (a square) – Represents a person or organization outside the scope and control of the system that provides data inputs and/or accepts data outputs. Data store (a shallow rectangle missing either its left or right side) – Data at rest, awaiting future access by a process or between process invocations. Real-time link (two-headed arrow with a kink or double bend) – A special type of data flow representing two-direction data movement between a process and an external agent as the process is executing. 3. How does an analyst determine whether a person or organization should be represented on a DFD as an external agent or by one or more processes? The key issues are system scope and degree of control. If the system has little or no control over the actions of a person, program, or organization, the person or organization should be represented as an external agent (for example, a customer, bank, or governmental agency). If the system has substantial control over the person, program, or organization, the person or organization can be represented using processes, data flows,
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Solutions_06 - Systems Analysis and Design in a Changing...

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