Systems Analysis and Development

Systems Development Documentation (SDLC)

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Sean Garcia

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What is it?
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Systems development documentation are documents that are created in the analysis and design phase of the SDLC. They specify the attributes or qualities of a system and serve to record the development of the new system or inform users or developers about the system being created.


  1. Context Diagrams

  2. Data Flow Diagrams

  3. System Manuals

  4. User Manuals

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Context Diagrams
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Image: A diagram of a System Context Diagram used for the high level analysis using Hatley-Pirbhai Modeling. Attribution: ​English Wikipedia user Chrislk02. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.


A context diagram is a graphical representation of data flow into and out of a system. It emphasises the source and sink of data and what data is flowing. Context diagrams only show data flows beyond the system boundary with external entities and therefore do not show processes or datastores.


They show the external entities (in rectangles), the system (in a circle) and the flows of data (lines with arrow indicated direction of data flow).


The context diagram allows us to understand the part of the system we have control over. We look further into the system when we look at the level 0 DFD (explained below). We can control aspects within the system but have no control over the external entities that interact with our system.


RULES:


  • MUST include the word ‘system’ when labeling the system

  • End each data flow with the word ‘details’

  • Context diagram DOES NOT show processes or data stores inside the system

  • The circle for the system represents the system boundary

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Data Flow Diagrams (DFD)
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Image: This is a Level 0 Data Flow Diagram for the fictional company "AvisonPlay.com". Image created using Select SSADM Professional v4.1.2. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.


A data flow diagram is a graphical representation of data in and through an information system. DFDs are process centric and thus show an internal view of the data flows within the system boundary. Processes in a DFD may be represented at a higher level, with less detail, as in a Level-0 DFD. Or decomposed into an increased number of more detailed processes in Level-1 DFDs or Level-2 DFDs etc.


Rules for L0-DFD:

  • Processes MUST have at least one data flow in AND at least one data flow out

  • Process names MUST start with a verb and be numbered (1.0 etc.)

  • The process should be named relational to the system – not the external entity (eg “Process payment” rather than “Pay money”)

  • End each data flow with the word ‘details’


Data flows CAN go from:

  • External entity to and from a process

  • Data store to and from a process

  • Process to process

Data flows CANNOT go from:

  • External entity to or from a data store

  • Data store to data store

  • External entity to another external entity


Level 0 DFDs MUST be balanced with the Context Diagram for the same system


  • MUST have the same external entities in level 0 DFD and context diagram

  • MUST have the same data flows to and from the external entities and the system


Rules for L1-DFD:

  • Processes MUST have at least one data flow in AND at least one data flow out

  • Process numbers must match the process number from the level 0 DFD

  • External entities are NOT shown – just the data flows to and from them

  • Data stores are shown

  • Level 1 DFDs MUST be balanced with the Level 0 DFD for the same system

  • MUST have the same Data Flows in and out of the Level 1 DFD as the Level 0 DFD

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System Manuals
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Technical documents that are generally designed to help developers or technical users of a system (generally also called internal documentation).

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User Manuals
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Documents that are designed to help users of the system (generally also called external documentation). These users are usually non-technical people and only need to know how to use the system, not how it works.

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