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MIS lecture 7


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System Development Life Cycle (SDLC)
Systems development project
- planned undertaking
- large job
- produces new system

sucessful project requirements
- detailed plans
- organized, methodical sequence of tasks and activities
System Development Lifecyle (SDLC) PHASES
- analysis: understanding business needs
- design: conceptualizing computer-system solution
- implementation: construction, testing, and installation

Additional phases
- project planning
- support
Planning Phase
- define problem
- confirm project feasibility
- produce project schedule
- staff the project
- launch the project
Analysis Phase
- gather info
- define system requirements
- build prototypes for discovery of requirements
- prioritize requirements
- generate and evaluate alternatives
- review recommendations with management
Design Phase
- design and integrate the network
- design the application architecture
- design the user and system interfaces
- design and integrate the database
- prototype for design details
- design and integrate the system controls
Implementation Phase
- construct software components
- verify and test
- convert data
- train users and document the system
- install the system
Support Phase
- maintain the system
- enhance the system
- support users
Data Flow Diagram
- a graphical tool that analylsts use to depict the flow of data in an information system
- the system can be physical or logical, manual or computer-based
- one form of a process model
Process Modeling
involves graphically representing the functions, or processes, which capture, manipulate, store, and distribute data between a sstem and its environment and between componenets of a system

a data flow diagram (DFD) is a type of process model
Requirements Structuring
refers to the meaningful representation of an information system. this involves the representation of:
- the existing system
- the replacement system

requirements structuring involes the following:
- data flow within the system
- processing logic and timing of events
- structure of data within the system
Deliverables from Process Modeling
- a context diagram which proides the scope of the system
- dfd of the current physical system specify which people and technologies are used in which processes to move and transform data
- technology-independent or logical, dfds of the current system
Data Flow Diagramming mechanics
- four symbols used
- two standard sets of data flow symbols (gane and sarson; demarco and yourdon)
data flow (DFD symbol)
data in motion, moving from one part of a system to another
Data store(DFD symbol)
data at rest
physicl locaitons include a file folder or a computer based file
Process (DFD symbol)
is the work or actions performed on data so that they are transformed, stored, or distributed
Source/Sink (DFD symbol)
the origin and/or destination of the data

external entities, outside of the system
Context Diagram
highest-level view of the system - provides an overview of a system that shows the system boundaries, external entities that interact with the system, and the major information flows between the entities and the major information flows between entities and the system

- one and only one process
- external agents (sources and sinks) around the perimeter)
- external data flows also around the perimeter
- data flows between system sources/sinks
- the single process, labeled "0" represents the entire system
The level-0 diagram
a data flow diagram that represents a system's majojr processes, data flows, and data stores at a high level of detail

- each process has a number with ends in .0 (corresponding the the level number of the DFD)
The functional decomposition diagram
the iterative process of breaking the description or perspective of a system into finer and finer detail

each process or sub-process is a candidate for decomposition

level-n diagram is a DFD that is generated from n nested decompositions from a level-0
Balancing DFDs
conservation of inputs and outputs

process 1.0 (in the level-0 diagram) must have the same inputs and outputs when decomposed into a level-1 diagram

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