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 System A system is defined by its boundary The system boundary sets it apart from its environment Environment Boundary

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 System A system will consume resources from its environment These may be physical or conceptual Environment 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 We are interested in information There will be a Goal

Systems System The environment may be static Or it may be dynamic Environment Magnitude and rate of change are important

Systems System A system must be able to change to match its environment Change – To achieve its goal Environment Change – By reconfiguration of components/resources System

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

System Practical Solutions System Redesign the 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 ‘One person’s data is another person’s information’ McCleod, 1998

Communication General Communications Channel

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

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 It is clear that we cannot develop any part of the system in isolation

Structured Methods Existing System ERD Repository Existing Physical System DFD New System ERD Repository New Logical System DFD Convert to Logical View User Requirements Technical Options + Constraints New Physical System We therefore need to introduce a certain amount of iteration into our development process

The End Have a good one…

References Whiteley, D. (2004) Introduction to Information Systems, Palgrave, 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