System design
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This document discusses tools and techniques for system design, including logical data flow diagrams (DFDs) and data dictionaries. DFDs use simple graphical symbols to represent processes, data flows, external entities, and data stores in a system. They provide an overview of how data moves through a system. A data dictionary comprehensively defines all data elements in a system. Physical design and prototyping are also discussed as part of specifying hardware, software, user interfaces, and the overall implementation of a system.
System design
- 1. GROUP:-4
- 2. • Evaluation of alternative solutions to a business design. • Specification of hardware, software and communication technology for the selected solution. • Purpose : Devise means to meet all the business requirements detailed in the requirements report.
- 3. • LOGICAL DESIGN • PHYSICAL DESIGN • CONSTRUCTION • TESTING
- 5. • Translation of the user requirements into detailed functions of the system. • This is often conducted via modelling, which involves a simplistic representation of an actual system. • Pertains to an abstract representation of the data flows, inputs and outputs of the system.
- 6. • INPUT FILES:The files used to capture the input data. • PROCEDURES:The logical algorithms used to process the input. The procedures are later transformed into code written in a programming language. • OUTPUT FILES:The files that will be used to capture information that is the result of processing data.The files in which input of customers, employees, suppliers, job applicants or other parties are recorded. • USER DIALOG:The manner in which the user will interact with the
- 7. • INTERFACE: How the system will interact with other systems. • Interface decisions include- * Provisions for input of data and the information from the files of other systems. * Lookups in the other system for decision making. * Retrieval of data from other systems. * Output of data to other systems.
- 8. • Flowcharts use graphical symbols to illustrate a systems logical operations as well as physical parts involved. • There are symbols that represent pieces of hardware, such as terminals, disks, communication lines and also logical operations such as beginning and ending points of a process and points of decision making. • For over 50 years, systems analysts and programmers have used flowchart as a language. • It is an independent means of describing a systems logical sequence. • After detailing the logic of a process in a flowchart, programmers translate the logic into a computer program.
- 9. • There are different symbols to represent – events, process, hardware device etc. • Some of them are standardized by ANSI, others remain non standardized. • The multitude of symbols, use of non standard symbols, the use of too many things in the same chart have rendered flow charting less and less popular in recent years. • A simpler alternative to graphically represent information systems have been developed- Data flow diagrams
- 12. System design can be achieved with the help of tools and techniques. Several tools exist --- to design a system + graphically and pictorially represent the system We discuss 2 such tools: (a) DFD (b) Data Dictionary
- 14. Data Flow Diagrams A graphical tool Uses Communicating Structured Analysis Logical Requirement Analysis Existing & Proposed System Focus Simple Technique Provides an overview Describe flow
- 15. DFD’S describe the flow of data in a business operation. DFD elements (Uses only 4 symbols) : 1.External entities (Source/Sinks) 2.Processes 3.Data stores 4.Direction in which the data flows
- 17. External Entities A Rectangle represents an external entity They either supply or receive data They do not process data Includes individuals and groups of people that are external to the system Ex: customers, employees , other departments in the organization, or other organizations Source – Entity that supplies data to the system. Sink – Entity that receives data from the system. External Entities
- 18. Processes 1. STORES Stores demand note Delivery Slip Issue Slip Ex: Processing of data into information Application of data to decision making Any events / sequence of events --- in which data are either changed /acted on • A circle represents a process • Straight line with incoming arrows are input data flows • Straight lines with outgoing arrows are output data flows • Labels are assigned to Data flow. These aid documentation
- 19. Data Stores • Data can be written into the data store. This is depicted by an incoming arrow • Data can be read from a data store. This is depicted by an outgoing arrow • External entity cannot read or write to the data store • Two data stores cannot be connected by a data flow Data StoresD1 Data StoresD1 Data StoresD1 Writing Reading Any form of data at rest, it is a repository of data (storage) Ex: database
- 20. Data Flows • Data in motion • Marks movement of data through the system - a pipeline to carry data. • Connects the processes, external entities and data stores. • Generally unidirectional, If same data flows in both directions, double-headed arrow can be used. Data Flow
- 21. Rules of Data Flow • Data can flow from External entity to process Process to external entity Process to store and back Process to process • Data cannot flow from External entity to store Store to external entity Store to store External entity to external entity
- 22. Note : DFD’s represent only entities, processes, data stores and data flows– nothing else. They cannot represent hardware devices or types of reports nor are they meant to detail the logic of processes Adv.: use of only 4 symbols + simplicity
- 23. Data flow diagram of a sales bonus system
- 24. The process of calculating sales bonus Sales clerk : entity entering data (salesperson’s I.D.) It flow into a process - Bonus calculation--- receives data from salespeople database(data store) The result of the process--- Bonus amount for each salesperson --- information ---flows into a bonus file Later – company’s controller will use the information to generate bonus checks
- 25. DFD FOR A BOOK BORROWING SYSTEM
- 26. DFD’s are used both in analysis and design phases of system development. In analysis phase – DFD’s – Describe + illustrate-- ---- How existing system operates They are suitable for describing any IS even if it is not computer based. Pinpoint weaknesses, which process and databases can be automated etc.. Provide a logical blueprint for construction of a new system
- 27. Logical and Physical DFD • DFDs considered so far are called logical DFDs • A physical DFD is similar to a document flow diagram • It specifies who does the operations specified by the logical DFD • Physical DFD may depict physical movements of the goods • Physical DFDs can be drawn during fact gathering phase of a life cycle
- 28. DATA DICTIONARY It is the complete and comprehensive definition of the entire data elements in the system. It is the source document for the specification for all inputs , protocol ,outputs ,data structures ,database structures ,its metadata and algorithms. It is a data repository of all design data about the system. Several description formats are available.
- 29. • One such format requires that for each item the following information be stored in DD.: Name, Alias ,Use ,Description ,Additional information • DD’s come to rescue when system breaks down for some reason. • It normally serves the following purpose: 1. A summary of the documentation 2. A tool to reduce reduntancy of data 3. A background for I/O design 4. As a centralized control of all data in a system 5. As a controller of data integrity
- 31. PHYSICAL DESIGN • Graphical representation of a system showing the internal and external entities and the flow of data into and out of these. • It begins once the logical blueprint for the new system is ready. • A systems physical design process includes specifying the h/w and s/w needed to support it. • It relates to the actual input and output processes of the system.
- 32. • The 3 sub-tasks in physical design 1. User interface design 2. Data design 3. Process design • Physical design specifies where, how and by whom a system’s processes are accomplished and does not tell us what is being accomplished.
- 33. Prototyping process • The major disadvantage of physical design is that it is a time- consuming process that is prone to considerable errors and omission. • To overcome this limitation many analysts and designers prefer prototyping, a modern engineering based approach to design. • Prototyping is the process of quickly putting together a working model (a prototype) in order to test various aspects of a design, illustrate ideas or features and gather early user feedback.
- 35. Contd.. 1. Identify basic requirements • Determine basic requirements including the input and output information desired. Details, such as security, can typically be ignored. 2. Develop Initial Prototype • The initial prototype is developed that includes only user interfaces.
- 36. 3. Review • The customers, including end-users, examine the prototype and provide feedback on additions or changes. 4. Revise and Enhance the Prototype • Using the feedback both the specifications and the prototype can be improved. Negotiation about what is within the scope of the contract/product may be necessary.
- 37. ADVANTAGES • Reduces development time. • Reduces development costs. • Requires user involvement. • Developers receive quantifiable user feedback. • Results in higher user satisfaction. • Exposes developers to potential future system enhancements. • Missing functionality can be identified easily. • Encourages innovation and flexible designs.
- 38. DISADVANTAGES • Too much involvement of client, is not always preferred by the developer. • Too many changes can disturb the rhythm of the development team. • Long term maintenance can be expensive. • Information can be lost through so many improvement changes.
- 39. CONSTRUCTION • Construction begins once software developmental tools are chosen. • Professional programmers translate input, output and processes as described in flowcharts and data flow diagrams into programs. • When program module is completed it is tested. • When all the modules are completed and tested, the modules are integrated into one coherent program.
- 40. SYSTEM TESTING • In system testing the entire integrated system is tested. • The system is checked against the system requirements originally defined in the analysis phase by running typical data through the system. • The quality of output is examined and processing times are measured to ensure that the original requirements are met.
- 41. • Testing should include attempts to get the system to fail. • It is done so that many unforeseen snags can be discovered and fixed before the system is introduced. • If new system passes the tests, it is ready for introduction in the business units that will use it.