Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Lecture 9: Structured Systems Development MIS 160 Systems Development Life Cycle I

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Structured Development Based on the principles of: –top-down decomposition –process driven Structured programming Structured design Structured analysis

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Systems Development Life Cycle Waterfall Model Project Identification and Selection Project Initiation and Planning Analysis Logical Design Physical Design Implementation Maintenance

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Advantages of Structured Development Been used successfully for over 20 years Provides a clear framework that defines and divides important activities Can be applied to both small and large projects Division of labor is easier to facilitate

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Limitations of Structured Development Specification problems –assumes that development is a sequential process Changing requirements –requirements specified at the beginning –assumption that requirements will not change Conceptualization and visualization –document led methodology –volume of documentation can be huge Inaccuracy –there is only downward trend

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Approaches to Structured Development Gane and Sarson –uses data flow diagrams –data dictionaries, process descriptions, file layouts Yourdon and DeMarco –similar to Gane and Sarson –difference in the symbols that are used

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Data Flow Diagrams Process-oriented approach –examines inputs, outputs, and processes of a system –purpose is to show the flow of information through a system 4 Sets of DFDs: –Physical DFDs of current system: show how the current system works –Logical DFDs of current system: show what the system currently does –Logical DFDs of proposed system: show what the new system must do –Physical DFDs of proposed system: show how the new system works

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Structured Approach Sequence Hierarchical Chart Physical DFD current system (WHAT/HOW) Logical DFD current system (WHAT only) Logical DFD proposed system (revised WHAT) Physical DFD proposed system (revised WHAT/HOW)

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Hierarchical Chart Terms: –parent,child,sibling –functional primitive –control module

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Hierarchical Chart Main

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Data Flow Diagram (DFD) Purpose: communication with user Components: –external entities (sources, sinks) –processes (subprograms) –data stores (files) –data flows (forms)

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Gane & Sarson process data store source/sink data flow Yourdon Data Flow Diagram (DFD) Symbols

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Definitions Process –The work or action performed on the data Data store –data at rest –represents a physical location for a file (e.g., file folder, computer file) Data flow –direction in which data moves –labeled with a name for data in motion

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Definitions Source/sink –origin (source) of the data –destination (sink) of the data –sometimes referred to as external entities (outside of the system) Do not consider the following –interactions between sources and sinks –what source/ sink does with the information –design/redesign of source/sink –direct access of source/sink to stored data

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 A Simple Sample 1.0 Hospital Pharmacy System 2.0 Review Prescription Doctor Prescription Unfilled Order Info. Unfilled Response Prescription D1Patient File Tech Review Patient Info

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 DFD Rules: Processes No process can have only outputs. It is making data from nothing (a miracle). If an object has only outputs, it must be a source. No process can have only inputs (a black hole). If an object has only inputs, then it must be a sink. A process has a verb phrase label.

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 DFD Rules: Processes Member 1.0 Member information Recruit Members Black hole Member 1.0 Membership Recruit Members Miracle

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 DFD Rules: Data Stores Data cannot move directly from one data store to another data store. Data must be moved by a process. Data cannot move directly from an outside source to a data store. Data must be moved by a process which receives data from the source and places the data into the data store. Data cannot move directly to an outside sink from a data store. Data must be moved by a process. A data store has a noun phrase label.

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 DFD Rules: Data Stores Member D2 Memberships D1 Members Renewal notice D2 Memberships Member Renewal notice D2 Memberships Membership Information

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 DFD Rules: Sources/Sinks Data cannot move directly from a source to a sink. It must be moved by a process if the data are of any concern to our system. Otherwise, the data flow is not shown on the DFD. A source/sink has a noun phrase label. Member Member information Clerk

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Context Level 0 Department Staff Student Financial Office Course Registration System Course Information Course Offerings Fees data Enrollment Information Schedule

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Level 0 Maintain Course Offerings 2.0 Maintain Student Enrollment 3.0 Create Reports Department Staff Financial Office Student Course offering changes Course offering list Fee payment history D1Course offerings Available course req. Available courses. Schedule Course enrollment D2Enrollments Course enrollment req. Student schedule Enrollment information Report request Department Staff Report Available courses Course offerings D1Course offerings Course information 1.0

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Level 1: Process Obtain Report Type D2Enrollments Department Staff 3.2 Create Reports D1Course offerings Course information Enrollment information Report request Report Type

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Models and Modeling Models are frequently used for documenting functional requirements –Created during analysis activity phase called ‘define system requirements’ –Focus on events and things Models are used in both the traditional and object-oriented approach

Sylnovie Merchant, Ph.D. MIS 160 Section 2 Spring 2004 Models and Modeling Analyst describes information system requirements using a collection of models Complex systems require more than one type of model Models represent some aspect of the current system/ system being built