Tools And Techniques Of System Design Ppt

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SSAD; TOOLS & TECHNIQUES

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SSAD; TOOLS & TECHNIQUES

1. SSAD Tools & technique S
2. PRAGNESH DAVE : 1 SAHELI KHERATKAR :2 SUREKHA RASKAR :3 RASIKA PATIL : 4 RICHA KOTHARI : 6 MINAL CHAUHAN : 7 NAMRATA JEURKAR : 8 SNEHAL BARI : 9 ASHWIN PATIL : 10 MALVIKA BANSAL : 11 RASHMI MAHASKAR : 12 TASVIR ZAIDI :13 SHILPA TAHAKAR: 14 PRESENTED BY
3. Management Information System MIS is a system consisting of people, machines, procedures, databases and data models, as its elements. The system gathers data from the internal and external sources of a organization, processes it and supplies information.
4.  SSAD was introduced in 1981 as the standard method of analysis and design developed by CCTA (Central Computing and Telecommunications Agency) for UK Government projects  SSAD was made mandatory for all new information system developments in 1983 HISTORY
5.  Structured Systems Analysis and Design (SSAD) is an integrated set of standards and guides for the analysis and design of computer systems  It is an integrated set of standards and guidelines consisting of : Structural standards, which define the structure of a development project in the form of explicitly defined tasks, with clearly defined interfaces between them, and also the tangible products Structured Systems Analysis and Design
6.  Improves productivity  Improves flexibility  Improves quality by reducing error rates  Delivers the system to users on time  Prevents IT developers' bureaucracy  Delivers systems that meets user's needs Benefits Of SSAD
7. Disadvantages Of SSAD  The size of SSAD is a big hindrance to using it in all circumstances  There is a large investment in cost and time involved in training people to use the technique to come to terms with  There are lot of standards for the preparation and presentation of documents
8. Data Flow Diagram Data Dictionary Decision Tree Structured English Decision Table Tools of SSAD
9. Data Flow Diagram  Data Flow Diagram is a graphical representation of the logical flow of the data.  It helps in expressing the system's requirements in simple and understandable form  It is also known as a bubble chart.  Its aim is to clarify the system requirements and identify major transformations that will become programs in system design  It decomposes the requirement specifications down to the lowest level of details
10. DFD contains 4 graphic symbols for  Source/destination  Data flow  Process  Data store
11. Source/destination Sign: Square. Symbol: Meaning: source/destination Description: It represents source/destination of system data.
12.  Sign: Arrow  Symbol:  Meaning: Data Flow  Description : It identifies the data flow; it is a pipeline through which the data flows. Data Flow
13.  Sign: circle/ bubble  Symbol: Meaning: Process  Description: It represents a process that transforms incoming data flow into outgoing flow. Process
14.  Sign: Rectangle  Symbol:  Meaning: Data store  Description:It represents data store. Data store
15.  Processes should be named and numbered  The direction of flow is from top to bottom from left to right  The name of the data stores, sources and destination is in capital letter.  Process and data flows name have the first letter capital  When a process is explored / divided in lower level they are number properly Rules for constructing /drawing DFD
16. In case of payroll system to prepare salary statement for each employee data flow can be represented as- Employee Data Accounts Dept Payroll processing Salary statement Employee file Employee
17.  Though DFD is very effective when required design is not clear and the user requires only graphic representation but more than 10-12 processes will make system complex and difficult to understand. ADVANTAGE & DISADVANTAGE
18. Data Dictionary A data dictionary is a structured repository of data. It is a set of rigorous definitions of all DFD data elements and data structure  It supports documentation in a better way  It serves as a common database for programmer and can be also used for control purposes
19. THERE ARE THREE CLASSES OF ITEMS TO BE DEFINED: 1. Data element - the smallest unit of data that provides for no further decomposition. 2. Data structure - a group of data elements handled as a unit 3. Data flows/stores - data flows are nothing but data structures in motion, whereas data stores are data structures at rest.
20. Rules for constructing Data Dictionary  The terms used to describe data structures are always in capital letters Assigned names should be straightforward and user oriented  There should be names for every data flow, data store, data structure and data element  Consistency checks should be performed  Identification numbers of the process and their names should be mentioned in the data dictionary
21. STRUCTURED ENGLISH  Structured English aims at getting the benefits of both the programming logic and natural language  It uses logical construction and imperative sentences designed to carry out instructions for action  Decision are made through IF-THEN-ELSE statements  Its sentences should be precise, concise and clear in word and meaning
22. Example of Structured English A bank will grant loan under the following conditions :  If a customer has an account with the bank and had no loan outstanding, loan will be granted  If a customer has an account with the bank but some amount is outstanding from previous loans then loan will be granted if special approval is given  Reject all loan applications in all other cases
23. IF customer has a Bank Account THEN IF Customer has no dues from previous account THEN Allow loan facility ELSE IF Management Approval is obtained THEN Allow loan facility ELSE Reject
24. DECISION TREE  Clear graphic representation of the logic, which looks like the branches of a tree, called decision tree  Easy to construct, read and update  Turns a decision table into a diagram & is read from left to right  Can be used to verify logic in problem that involves few complex decisions.
25. Example: Computer dealer gets a trade discount of 35% if the order size is 6 or more PCs, whereas for orders from educational institutions and individuals, 15% discount is allowed on order of 6-19 PCs, 20% on orders for 20-49 PCs; 30% on orders for 50 PCs or more Dealer 6 or more 35% Less than 6 NIL DISCOUNT POLICY Educational Institution or individual 50 or more 30% 20 – 49 20% 6-19 15% Less than 6 NIL Decision tree
26. DECISION TABLE  A matrix of rows and columns that shows conditions and actions  Decision rules state the procedure to be followed when certain conditions exist.  Decision table are best-suited for dealing with complex branching routines, e.g., inventory control  A condition is usually given a value of 'Y' for 'Yes, if is true", 'N' for 'No' and a dash for 'Do not care' in each rule.
27.  Decision table consists of four sections. A condition stub at the upper left, a condition entry at the upper right, an action stub at the lower left, and an action entry at the lower right Questions are listed in the condition stub and the action stub outlines the action to be taken to meet each condition  Condition entry part contains the answers to questions asked in the condition stub and the action entry part indicates the appropriate action Condition Stub Condition Entry Action Stub Action Entry
28. In constricting a decision table, the following rules are observed:  A decision should be given a name to be written at the top left of the table  The logic should be independent of the sequence in which the condition rules were written but the action takes place in the order in which the events occur  Consistent and standardized language should be used  Duplication of the terms should be avoided to the maximum extent
29. TECHNIQUES OF STRUCTURAL SYSTEM ANALYSIS AND DESIGN Data Flow Modeling (DFM) Logical Data Structure (LDS) Entity Life History (ELH)
30. DATA FLOW MODELING  Pictorial representations of systems have long been acknowledged as being more effective than narrative  Conventional flowcharts have been used for many years, with considerable advantages over narrative Here are some examples:  System flowchart (for high-level system description)  Clerical procedure flowchart (for low-level description)  Computer run chart
31. Disadvantages  They confuse the logical aspects of the system (what is done) with the specific physical implementation (how it is done)  They do not allow any easy transition from high-level broad description to detailed low-level description  They are "procedure orientated", placing the greatest emphasis on procedures in the system, rather than on data which appears only occasionally on the flow chart
32. LOGICAL DATA STRUCTURE:  The pictorial representation of entities and the relationships between them is called an Entity model  A current system Logical Data Structure (LDS) is a form of Entity model which represents entities and their relationships in the current system environment
33. Entities  For those unfamiliar with the term "entity" its nearest equivalent in more familiar terminology is "file"  A working definition, suitable at this stage, is "something about which an organization keeps data"  An entity may be physical, e.g. Person, Building, Machine etc, or conceptual, e.g. Cost centre, project, etc.
34. ENTITY LIFE HISTORY  Entity Life Histories (Elhs) look at a system from a third viewpoint, providing a means of representing how entities change within a system with the passage of time  Elhs start with the creation of an entity, record the sequence of changes which take place during its life within the system and end with its removal from the system
35. ELHS & PROCESSES Elhs are used to help define :  the logic associated with update processes  an examination of processes provides a starting point to describe ELH concepts and terminology  ELHS are concerned with update processes only
36.  Facilitate more focus on reducing maintenances and time effort in system development  Integrate change when needed  Widely useful in industry - proven techniques  Part of career growth in IT - lots of interesting and well-paying jobs!  Shows a steep increase in demand for systems analysis skills CONCLUSION