System Design Mr Ahmad AlGhoul learning Objectives Discuss

System Design - Mr. Ahmad Al-Ghoul

learning Objectives § Discuss guidelines and objectives for systems design Avicenna System Analysis and Design System Design 2

Introduction n n If management decides to develop the system in-house, then the transition to the systems design phase begins In a smaller company, you will assigned full responsibility for the design task In larger company you will be a member of the design team System design is the first phase of the system development life cycle in which you and the user develop a concrete understanding of how the system will operate Design phase n n Avicenna Decide how to build the system Create system requirements that describe technical details for building the system System Analysis and Design System Design 3

Systems Design Guidelines n Preparing for Systems Design Tasks n n Avicenna It is essential to have an accurate and understandable system requirements document System requirements document is the starting point for the system design phase Errors, omissions, ambiguities, and other problems will affect the quality of the finished product Before proceeding to the design phase, you must be certain that you performed a complete and accurate system analysis and communicated the results in your system requirements document System Analysis and Design System Design 4

Systems Design Guidelines n The Relationship between Logical and Physical Design n n The logical design defines the functions and features of the system and the relationships among its components Logical design done during the system analysis phase n Logical design includes n n n Avicenna Output that must be produced by the system Input needed by the system Process that must be performed by the system, without regard to how tasks will be accomplished physically System Analysis and Design System Design 5

Systems Design Guidelines n The Relationship between Logical and Physical Design n n The physical design of an information system is a plan for the actual implementation of the system The physical design is built on the system’s logical design and describes a specific implementation System design usually begins after completing system analysis phase Some overlap is possible, you might return to fact-finding if you discover that you overlooked an important issue, if user have significant new needs, or if legal or governmental requirements change n Physical design describes n n n n Avicenna Input design Output design Interface design Report design Actual processes of entering, verifying, and storing data Physical layout of data files Sorting procedures System Analysis and Design System Design 6

Systems Design Guidelines [1] n The systems analyst must understand the logical design of the system before beginning the physical design of any one component Avicenna System Analysis and Design System Design 7

Systems Design Guidelines n n Design phase is not a series of clearly defined steps because the components of the system are interdependent You might start with one component, or you can work on several components at the same time Avicenna System Analysis and Design System Design 8

System Design Objectives n The goal of systems design is to build a system that is effective, reliable, and maintainable n n A system is effective if it defined requirements and constraints, accepted by users, and support the organization’s business objectives A system is reliable if it adequately handles errors, input errors, processing errors, hardware failures, and human mistakes. n n A system is maintainable if it is well designed, flexible, and developed with future modifications in mind n Avicenna An approach to building a reliable system is to plan errors, detect them as early as possible, allow for their correction, and prevent them from damaging the system Modification necessary to correct problems, to adapt to changing user requirements, to enhance the system, and to take advantage of changing technology System Analysis and Design System Design 9

System Design Objectives System design considerations n User Considerations n System must be user friendly n Carefully consider any point where users receive output from, or provide input to, the system n n Anticipate future needs of the users, the system, and the organization n n hard-coded solution is straightforward, but its not a good choice when the organization want to add anther rules Provide flexibility n Avicenna The user interface must be easy to learn and use Input processes should be well documented, easy to follow, intuitive, and forgiving of errors Output should be attractive and easy to understand there are many issues to take into consideration to make the system more flexible System Analysis and Design System Design 10

System Design Objectives System design considerations n Data Considerations n n Data should be entered into the system where and when it occurs because delays cause data errors Data should be verified when entered to catch errors immediately n n Automated methods of data entry should be used whenever possible n Avicenna The system also should allow corrections at any time Automated data entry methods reduce input errors and improve employee productivity System Analysis and Design System Design 11

System Design Objectives System design considerations n Data Considerations n Access for data entry should be controlled and all entries or changes to critical data values should be reported n n Avicenna Dollar fields and many volume fields are considered critical data fields Critical data volume include the number of checks processed, the number of insurance premium payments received Report that trace the entry of and changes to critical data values are called audit trails and are essential in every system Every instance of entry and change to data should be logged System Analysis and Design System Design 12

System Design Objectives System design considerations n Data Considerations n Data should be entered into a system only once n n Data duplication should be avoided n Avicenna If there are some data needed by two systems, you should design program interface between the systems so data can transfer automatically In some cases we need to store the same data with different records, those data must stored once, so if we need to update the data we will update it once System Analysis and Design System Design 13

System Design Objectives System design considerations Architecture considerations n Use a modular design n n n Avicenna In a modular design, you create individual processing component, called modules, which connect to a higher level program or process In structural design each module represents a specific process or sub process shown in a DFD and documented in a process description In object-oriented design, object classes are represented by code modules Design modules that perform a single function are easier to understand, implement, and maintain Independent modules provide greater flexibility because they can be developed and tested individually Modular design is helpful especially when developing large scalesystems System Analysis and Design System Design 14

System Design Objectives n Design Trade-Offs n n n Avicenna Design goals often conflict with each other In the system design phase, you must analyze alternatives and weight trade-offs Most design trade-off decisions that you will face come down to the basic conflict of quality versus cost Avoid decisions that achieve short-term savings but might mean higher costs later Each trade-off must be considered individually, and the final result must be acceptable to users, the systems staff, and company management System Analysis and Design System Design 15

Sequence Summary n n n System design is the first phase of the system development life cycle in which you and the user develop a concrete understanding of how the system will operate System requirements document is the starting point for the system design phase The logical design defines the functions and features of the system and the relationships among its components The physical design of an information system is a plan for the actual implementation of the system The goal of systems design is to build a system that is effective, reliable, and maintainable Systems design guidelines and suggestions, including user considerations, data considerations, and processing considerations Avicenna System Analysis and Design System Design 16

Sequence Summary n In this Sequence we have n Described the tasks needed to prepare for system design phase n Explained the Relationship between Logical and Physical Design n Explained the system design objectives n Explained the systems design guidelines and suggestions, including user considerations, data considerations, and architecture considerations n Described the design trade-offs Avicenna System Analysis and Design System Design 17

Reference [1] System Analysis and Design, Sixth Edition Authors: Gary B. Shelly, Thomas J. Cashman and Harry J. Rosenblatt Publisher: SHELLY CASHMAN SEWIES. Avicenna System Analysis and Design System Design 18