Structured Systems Analysis and design method

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Structured Systems Analysis and design method

• Caroline M Ashworth

Group 6 Pratiksha Kadam
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SSADM basic principles

• Data-driven
• - all applications have an underlying, generic
  data structure which changes little over time
• - underlying structure is developed from an
  early stage, checked against the processing and
  reporting requirements

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Differentiation between logical and physical

• Logical v/s physical
• - hardware/software independent oriented logical
  design is produced which can be translated into
  an initial physical design
• - helps the developers to address one problem at
  a time
• - computer illiterate can design and validate a
  logical specifications or design

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Views of SSADM

• The logical data structure
• Data flow into and out of the system and is
  transformed within the system (data flow diagram)
• How the systems data is changed by events over
  time ( entity life histories)

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Top-down and Bottom-up

• In the early stages of a project, top down
  techniques such as data flow diagramming and
  logical data structures are used
• In the logical design stage bottom up techniques
  provide more detail and reconciled with the
  top-down views.

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User involvement

• User involvement is emphasized from the early
  stage to match users requirements at early stage
• Easily understandable, non technical diagrammatic
  techniques are used
• Informal walkthroughs and participation in formal
  quality assurance reviews
• Ideally user representative can work full time
  within development team

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Cont

• Quality Assurance
• - reviews and walkthroughs are encouraged
  throughout method. The end products are
  scrutinized for quality, completeness,
  consistency and applicability by users,
  developers
• Self Documenting
• - documentation is completed at the relevant
  time within the project.

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Overview of SSADM

• Structure of the Method
• - each stage is broken down into a number of
  steps which define inputs, outputs and tasks to
  be performed.
• - current system is studied to build the
  required specifications of the system
• - the detailed design is completed at logical
  level before implementation issues are addressed.
• - logical design is converted into physical
  design

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Stage one

• Analysis system operation and current problems
• - the current system is analyzed to learn the
  terminologies and the function of users
  environment
• - the data required by the system can be
  investigated
• - the underlying structure of the data doesnt
  change much over time
• - If there is no current system, then project is
  initiated begins to document the new requirements

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Stage two

• Specifications of Requirements
• - the current system view built gives just what
  the system does without any indication of how
• - analyst can then decide on current functions
  and new ones required
• - Business system option then decides on how the
  business can be organized to make the best use of
  the system.

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Stage three

• Selection of Technical Options
• - team decides on the requirement of new
  hardware, different implementation options,
• - options are costed out and the benefits are
  weighed. Helps in tendering for the final system

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Stage four

• Rational analysis is applied to groups of data
  items to cross check the data definitions
• The final data design is checked against logical
  processes developed in stage five

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Stage five and six

• Stage five Logical process design
• - definitions developed in stage two are
  expanded to low level details to build the system
• Stage six Physical Design
• - the complete logical design is converted into
  a design that will run on the target environment

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Structured techniques

• Logical data structures (LDS)
• - describes what information should be held by
  the system
• - LDS is created for the current system and
  extended to meet the requirements of the new
  system

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Data Flow diagrams

• Information flow within a system
• Data flow are means of boundary definition
• The construction and cross check of the diagrams
  ensures correct information flows within the
  system
• Four data flow are drawn
• - The current physical
• - the current logical
• - business system options
• - selected business option and logical data flow
  diagrams developed, the new system is developed

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Entity life histories

• Models the systems data change over time by
  events
• The effects of the events upon each entity from
  the logical data structure are modelled

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Logical Dialogue outline

• A logical dialogue outline is produced for each
  non trivial event or enquiry identified during
  analysis
• Its possible to add the requirements for the time
  taken at each stage of the dialogue, where user
  will be required to make decisions.

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Relation data analysis

• A collection of data items defined without any
  reference to logical data structures
• Normalization consists of progression from the
  original data through refinements
• It is done by some rules, gives a set of data
  corresponding to the entities on the logical data
  structure

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First Cut rules and Physical design control

• First cut design is tuned using a process called
  physical design control, calculates the time
  taken to execute certain critical transactions
  and modifications are performed in the design

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Quality Assurance reviewing

• Emphasis on quality assurance reviews at the end
  of each stage
• Before the review all participants receive an
  invitation to the review meeting, the relevant
  aspects of the diagram are explained if unaware
• The review meeting an analyst from the project
  team walks through the documentation being
  reviewed and invites comments. A list of errors
  is compiled. If there are numerous errors then a
  date of another quality assurance review is set.
• After the review- necessary modifications are
  made to the documentations and circulated to the
  members of the review team.

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Project Estimating

• Guidelines for estimating projects
• Estimating guidelines are applied to initial data
  flow diagrams and logical data structure
• Estimates derived at the beginning will not be
  accurate and will be refined over the period

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Documents and Forms

• Documents are entity description and elementary
  function descriptions
• Forms are problem/requirement list and function
  catalogues
• An entity matrix also helps identify
  relationships between entities as an initial step
• Problem requirement list checklist of all the
  factors to be accounted in the project
• Analyst has to store requirements gathered from
  the user in logical terms

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Automated support for SSADM

• Automatic production of documents
• Assistance in creating and amending SSADM
  diagrams
• Enforcements of diagram syntax
• Enforcement and help with the rules of methods
• Consistency and completeness checking
• Traceability of specifications through to logical
  and physical design
• Automatic generation of elements of the design
• Presentation of the information in different
  formats and combinations
• Integration of diagram information with data
  dictionary informations

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Comparison with Yourdon method

• Yourdon method has data flow diagrams and logical
  view between entity relationship
• The main difference is no structure of steps,
  stages, deliverable and detailed task list in
  Yourdon

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Arthur young information engineering method

• This method has no of steps and stages leading
  from strategy to construction with emphasis on
  data model
• SSADM has detailed task lists with define inputs,
  outputs and activities whereas AY gives more
  freedom to choose
• SSADM uses third view in analysis provided by the
  entity life history techniques

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Questions?