IS Design(312)Lecture 1 (IntroductionToSysDesign)

PowerPoint Presentation: 

1 Introduction to Information Systems Design (IS 312) Abdisalam Issa-Salwe Taibah University Information Systems College of Computer Science & Engineering Lecture 1

Topic list: 

2 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Topic list Understanding the processes, methods, techniques and tools designing computer business information systems Exploring a systematic methodology for analysing a business problem or opportunity

About Systems: 

3 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems Systems approach emerged in 1950s more analytical approach to management and problem solving three parts: Systems philosophy: View things as systems, interacting components working within an environment to fulfill some purpose Systems analysis: problem-solving approach Systems management: Address business, technological & organizational issues before making changes to systems

About Systems (cont…): 

4 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) “... a set of elements standing in inter-relation” Ludwig von Bertalanffy Systems theory was proposed by the biologist Ludwig von Bertalanffy. Instead of reducing a biological system, such as a plant or animal, to parts (organs or cells), systems theory accepts that each identifiable component is related to other parts. The entire system works together but each sub-system is identified by the unique activity that occurs within it.

About Systems (cont…): 

5 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) A set of interrelated components working together Have a purpose, achieve a common goal A regularly interacting or interdependent group of items forming a unified whole. An organized set of doctrines, ideas, or principles, usually intended to explain the arrangements or working of a systematic whole An organized or established procedure. Harmonious arrangement or pattern An organized society or social situation regarded as stultifying establishment.

About Systems (cont…): 

6 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) A system is an organised assembly of components. Organised means there exist special relationships between the components. The system does something i.e. it exhibits a behaviour unique to the system. Each component contributes towards the behaviour of the system and is affected by being in the system. The behaviour of the system is changes if any component is removed or leaves. Groups of components may form subsystems. The system has an outside - an environment - which provides inputs into the system and receives outputs from the system.

About Systems (cont…) : 

7 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) Model of the observed situation: helps to understand what might be going on. Looking at systems working as cells - inputs, outputs, processes within the cell, purpose of the cell Relationship with thinking of engineering production - raw materials, finished product, production processes, overall design and purpose Systems engineering - how to solve a design problem elegantly

About Systems (cont…) : 

8 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) Biological systems Physical systems Man-made systems

About Systems (cont…): 

9 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University About Systems (cont…) Man-made systems include such things as: Social systems: organizations of laws, doctrines, customs, and so on. An organized, disciplined collection of ideas. Transportation systems: networks of highways, canals, airlines and so on. Communication systems: telephone, telex, and so on. Manufacturing systems: factories, assembly lines, and so on. Financial systems: accounting, inventory, general ledger and so on.

Systems environment and boundary: 

10 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Systems environment and boundary The environment it is that part of the world that can be ignored in the analysis except for its interaction with the system. It includes: competition, people, technology, capital, raw materials, data, regulation and opportunities. The boundary defines the difference between the environment and the system The correct boundary is a function of the problem under consideration

Characteristics of systems: 

11 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Characteristics of systems Goal oriented - Systems are goal oriented (either by evolution or design) Inputs - Systems have inputs from their environment. Outputs - Systems have outputs to achieve their goals. Process – transforms input into output. Feedback – reintroduces a portion of the output of a system as an input into the same system.

System boundary: 

12 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University System boundary Dividing line Placed based on the purpose: usually not a fixed line Control or redesign within the boundary Environment outside the boundarys Boundary – the perimeter or line of demarcation between a system and the environment. Connections – transmit the flow of material and information that coordinate the system’s components.

Elements of a System: 

Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Elements of a System Purpose: the reason it exists. The reference point for measuring its success Subsystems: parts or elements which perform specified tasks that are compatible with the goals of the larger system of which these are parts. Environment: the people, facilities, rules, policies, and regulations that surround a system.

Characteristics of a System: 

14 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Characteristics of a System Components Irreducible part or Aggregation of parts that make a single “object” (e.g., a modem is a single object that is actually made of lots of circuits and switches, etc.) Aggregations are called “subsystems” Interrelations Function of one component ties it to the function of others within the system System working towards some purpose

Characteristics of a System (cont…): 

15 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Boundary What separates from its environment System lies within the boundary Purpose Overall goal or function System working towards a purpose. Without purpose, subsystems fail Characteristics of a System (cont…)

Characteristics of a System (cont…): 

16 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Environment Made up of components as well The impact of the system to the environment as outputs. Interfaces Where the system meets its environment Also exist between subsystems Characteristics of a System (cont…)

Characteristics of a System (cont…): 

17 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Constraints Limitations Can be internal (e.g., resources) Can be external (e.g., rules and realities) Constraints are limits to what a system can do as a result of external rules and realities or internal decisions Input A system takes input from its environment in order to function Starts the cascade of the system Characteristics of a System (cont…)

Characteristics of a System (cont…): 

18 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Output Output is what a system returns to its environment as a result of achieving its purpose Outputs are the data or information result of the processing Characteristics of a System (cont…)

Component Decomposition: 

19 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Component Decomposition Break system into subsystems Components of subsystem may form more subsystems Often subsystems are easier to understand, create, modify

System types: 

20 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University System types One of the most common way to classificate systems are in open versus closed systems . A closed system is defined in physics as a system which is self-contained. It does not exchange anything with its environment. … isolated from its environment and is independent of it. An open systems exchange information, material, or energy with the environment, including random and undefined inputs. A system connected to and interacting with its environment

System types (cont…): 

21 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University System types (cont…) There are several way to classify system: Deterministic and probabilistic: In a deterministic system is the interaction among the parts known with certainty. In a probabilistic system is always a degree of error attached to the prediction of what the system will do. Self-organising system is one which adapts and reacts to a stimulus.

The stages of design: 

22 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University The stages of design Design activity involves developing a series of models The most important models for the designer are the systems implementations model and the program implementation model. The systems implementations model divide into a processor model and a task model

Stages of Design: 

23 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Stages of Design The processor model: At this level, the systems designer decides how the essential model should be allocated to different processors and how those processors should communicate with one to another The task model When the processes and stores have been allocated to processors, the systems designer assign processes and data stores to individual propose tasks The program implementation model At the level of an individual task, the systems designer has already accomplished two level of process and data storage allocation.

Tools and Techniques of design: 

24 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Tools and Techniques of design The design of information systems requires that systems analysts understand how information flow in an organization How it relates decision making, and how it contributes to organizational goals and objectives. While data are being collected on the problem environment and the analyst is learning about the information needs of the user, rough ideas about the way to improve the information function are being formulated in the analyst’s mind.

Key Definitions: 

25 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Key Definitions The purpose of the design phase is to translate the “what” of the analysis phase to the “how” of new system development Logical DFDs and ERDs are converted into physical DFDs and ERDs Structured English is turned into psuedocode and CASE repositories are expanded

Design Strategies: 

26 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Design Strategies Custom development (build from scratch) Purchase and customize Outsource development

Classical Mistakes: 

27 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Classical Mistakes Reducing design time Feature creep Silver bullet syndrome Switching tools in mid-project

Custom Development: 

28 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Custom Development Pros Cons Allows flexibility and creativity Builds technical skills and functional knowledge in-house Requires significant time and effort May exacerbate existing backlogs May require missing skills Often costs more Often takes more calendar time Risk of project failure

Systems Integration: 

29 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Systems Integration Building systems by combining packages, legacy systems, and custom pieces Integrating data is the key Selecting a Design Strategy: Consider each of the following: Business need In-house experience Project skills Project management Time frame

Designing Specifications: 

30 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Designing Specifications By definition, analysis and design are two separate activities. The two development activities are so intertwined that no one can say exactly when analysis ends and design begins. The design of an appropriate information system requires that analysts understand the goals and objectives of management. They must also be sensitive to changes that may occur to these goals and objectives over time in response to shifts in the competitive environment.

Moving From Logical to Physical Models: 

31 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Moving From Logical to Physical Models Key Definition In contrast to the logical DFD and ERD which shows the business view of the new system, the physical DFD and ERD will show the implementation details and how the system will work.

Structured System Analysis: 

32 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Structured System Analysis Logical Data Modeling ; This is the process of identifying, modeling and documenting the data requirements of a business information system. A Logical Data Model consists of a Logical Data Structure (LDS - The SSADM terminology for an Entity-Relationship Model) and the associated documentation. LDS s represent Entities (things about which a business needs to record information) and Relationships (necessary associations between entities).

Structured System Analysis (cont…): 

33 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Structured System Analysis (cont…) Logical modeling deals with gathering business requirements and converting those requirements into a model. The logical model revolves around the needs of the business, not the database, although the needs of the business are used to establish the needs of the database. Logical modeling involves gathering information about business processes, business entities (categories of data), and organizational units. After this information is gathered, diagrams and reports are produced including entity relationship diagrams, business process diagrams, and eventually process flow diagrams.

Phases of Design (cont…): 

34 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Phases of Design (cont…) Logical Design: The objective of this phase is the development of a design which is directed by an abstract machine and operating environment. This model contains the highest amount of quality and quality components as we were able to incorporate, with the time and talent available.

Phases of Design (cont…): 

35 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Phases of Design (cont…) Physical Design: The objective of this phase is the creation of a blueprint of the system This blueprint is complete and correct and accurately describes every aspect of the system to be developed

The Physical DFD: 

36 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University The Physical DFD Contains the same components as the logical DFD The same rules pertaining to balance and decomposition apply Contains additional details describing how the system will be built

Steps to Create the Physical DFD: 

37 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Steps to Create the Physical DFD Add implementation references Draw a human-machine boundary Add system related data stores, data flows and processes Update data elements in the data flows Update the metadata in the CASE repository

Contrasting Logical and Physical DFDs: 

38 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Contrasting Logical and Physical DFDs

The Physical ERD: 

39 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University The Physical ERD Contains the same components as the logical ERD The same rules pertaining to cardinality and modality apply Contains additional details describing how the data will be stored, in a file or database table

Steps to Create the Physical ERD: 

40 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Steps to Create the Physical ERD

Designing Specifications: 

41 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Designing Specifications The goals of Structured design are accomplished through the consistent implementation of specific philosophical views At the heart of this method is the notion that a program, a group of programs, or a group of systems is nothing more than a collection of functions

Design goals and objectives: 

42 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Design goals and objectives The design objectives specified in the user implementation model are the quality of the design The ability of the programmers to implement a high-quality, error-free system depends very much on the nature of the design created by the designer The ability of the maintenance programmers to make changes to the system after it has been put into operation and to the expanded system depends on the quality of the design

A poor analysis job is going to cause problems: 

43 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University A poor analysis job is going to cause problems Problem Effect on Design Dataflow diagram not balanced Interface Problems ‘Fuzzy’ process name Need to repartitioning Dictionary not correlated with dataflow diagrams Duplicates and aliasing and interface problems Dataflow diagrams not correlated with dictionary Duplicates and aliasing and interface problems Pseudo code not validated Logic errors Pseudo code not correlated with dictionary Data aliases, interface problems

PowerPoint Presentation: 

44 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University

Design issues: 

45 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Design issues Security: The end user may have security processor and sensitive data in protected location Reliability: The end user will normally specify reliability requirements for a new system Political requirements that dictate the placement of some and operational constraints: The hardware configuration may also be influenced by political constraints imposed directly by the end user

Discussion Questions: 

46 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Discussion Questions What are the main components of a computer-based information systems? Why is systems analysis and design is necessary? What is the role of users during systems analysis and design? What is a system? Why we apply design as a system? What are the components of a system?

Reference: 

47 Abdisalam Issa-Salwe, College of Computer Science & Engineering, Taibah University Reference Alan Dennis and Barbara Haley Wixom, Systems Analysis and Design, John Wiley & Sons, Inc. Abdisalam Issa-Salwe, SSM Notes, Thames Valley University.