Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Further Systems Analysis Plan • Introduction • Structured Methods – Data Flow Modelling – Data Modelling – Relational Data Analysis – Further Data Modelling – Further Systems Analysis Topics Information and Systems …and Information Systems Systems • There is no universally accepted definition of a system • Properties that are generally considered part of a good definition – An organised or complex whole – An entity that consists of independent parts – These parts are affected by being part of the system and are changed by being removed from the system – A collection of related activities working together to achieve a common objective – An assembly of parts that have been identified by an individual as being of special interest Systems A system is defined by its boundary Environment System Boundary The system boundary sets it apart from its environment Systems Different observers will view a system in a different way There may be a different physical context – e.g. CD Hotels Systems Different observers will view a system in a different way It may be that the difference is more conceptual It’s the same system but it is described using a different set of symbols Systems Different observers will view a system in a different way Both of these situations can cause problems for the systems analyst Systems A system will consume resources from its environment Environment System These may be physical or conceptual A system will also produce some output Biological Systems • Frogs Inputs Outputs Natural Systems – Goal unclear Man Made Systems • Inputs – – – – Physical Resources People Information Money • Outputs – – – – Physical Goods People Information Money There will usually be some transformation There will be a Goal We are interested in information Systems The environment may be static Environment System Or it may be dynamic Magnitude and rate of change are important Systems A system must be able to change to match its environment Environment System Change – To achieve its goal Change – By reconfiguration of components/resources Impact on Development • We must be aware of the system’s environment – Static/Dynamic – Rate of change • The system must be able to – React to change – Reduce the effect of change Law of Requisite Variety • A system must be as complex as the environment in which it operates • Therefore it must be able to reconfigure it’s resources to react to environmental changes Practical Solutions Redesign the system System Add new components to the system Create Adaptive Systems Information Definitions • ‘Information is data which has been processed in such a way that it has meaning to the person who receives it, who may then use it to improve the quality of decision making.’ CIMA Information Management Study Text • ‘‘Information’ refers to the aggregation of data that - when it is interpreted and understood - provides systems users with knowledge of some kind.’ Edwards et al., The Essence of Information Systems • ‘Information is raw data converted into a form to enable the user to make a decision in response to a business need.’ Thomas and Ballard, Business Information • ‘Information is data that have been processed in such a way as to be useful to the recipient.’ Rowley, Strategic Management Information Systems and Techniques Information • Structure – Data is brought together to have some meaning • Processing – The data must be processed to give it structure • Communication – Information should communicate something to the recipient Information - Structure • See TopDog examples Information - Process • In order to become information, data must undergo some form of Transformation, Processing or Formatting Data Process, Format or Transformation Information • ‘One person’s data is another person’s information’ McCleod, 1998 Communication • General Communications Channel Source Destination Message Transmitter (encoder) Noise Received Message Channel Signal Signal + Noise Receiver (decoder) Information • Structure • Processing • Communication • Similar properties to systems • In order for information to exist there must be a system to produce it • We control information by systems development Review of SAD The Problem of Development • Development views of the system – System development is complex problem – We handle complexity by dividing the problem • Process View • Data View • Dynamic View Information System Architecture 2 5 1 6 4 3 7 1. Users • Users send commands and instructions across the user interface • Users send and receive data across the user interface • The interface will also implement security controls (e.g. log in passwords etc) 2. User Interface • How do we present information to our users? • How do we collect data? • UI may be written in languages such as Visual Basic • May even be written in HTML with scripting languages 3. User Interface • Technology Used – HCI • Usability Issues – Process and data Design • Navigation – State Transition Diagram • Design – GUIIN real systems People and Paper also form part of this interface (e.g. phone banking) 4. Processes • The business processes are described using DFDs and other models (ELH, STD). • They will be implemented in a programming language such as Visual Basic, Java, C++ • Should keep their implementation separate from the GUI 5. Data Interface • There is an interface between the business processes and the data • This is often implemented using SQL (structured query language) • If a file system other than an RDB is used then this interface must be implemented by some other means. 6. Database • The database is defined in the data model • Described in the process model – via data dictionary • Usually implemented in a Relational database – Oracle, Access, MySQL • May also be implemented as paper files or electronic files (e.g. HTML) 7. System Boundary • Defines the scope/context of the system – Identified in the DocFD and Context Diagrams • All access to the system should be via the user interface • Some users may be other systems • All interfaces need to be carefully defined to avoid security, and other problems Development Process • What is the scope/context of the system? • What must it do? What are its outputs? – Requirements Gathering – Rich Pictures/DFDs • What Processes are needed to do it? • What data do the processes require? – Requirements Analysis – DFDs/ERDs Development Process • How do we store the data (relational DB)? – Database Design - Normalisation • How will the users use the system? – Interface Design – State/Transition Diagrams Information System Architecture 2 5 1 6 4 3 7 It is clear that we cannot develop any part of the system in isolation Structured Methods User Requirements Existing Physical System DFD Convert to Logical View New Logical System DFD Repository Repository Existing System ERD New System ERD We therefore need to introduce a certain amount of iteration into our development process Technical Options + Constraints New Physical System The End • Have a good one… References • Whiteley, D. (2004) Introduction to Information Systems, Palgrave, 2004. • Lejk, M. and D. Deeks (2002) Systems Analysis Techniques, Addison Wesley 2002 • Mason, D. and L. Willcocks (1994), Systems Analysis, Systems Design, Alfred Waller, 1994. References • Yeates, D. and T. Wakefield (2004) Systems Analysis and Design, FT/Prentice Hall 2004 • Gane, C. and T. Sarson (1979) Structured Systems Analysis, Prentice Hall, 1979 • Eva, M (1994) SSADM Version 4: A users guide, McGraw hill, 1994 References • DeMarco, T. (1979) Structured Analysis and System Specification, Yourdon, 1979 • Royce, W. (1970) Managing the development of large software systems, In: Proceedings of IEEE WESCON, 1970 pp1-9. • Connolly, T. and C. Begg (2000) Database Solutions, Addison-Wesley, 2000