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CSE1204 - Information Systems 1
Revision
Subject Overview System concepts and information systems Systems development and the SDLC Information gathering Modelling Process modelling using DFDs Low-level processes: minispecs
Subject Overview System design principles Communicating using documentation and
presentations Working in teams Ethics and professional practice Roles in the SDLC Project management Quality - product and process Types of information systems
System concepts and information systemsA system: An inter-related set of components that
interact to accomplish goals system elements
• components, inter-related components, a boundary, a purpose, an environment, interfaces, input, processing, output, feedback, constraints
Information systems An Information System is a formal
arrangement of people, data, processes integrated to help manage complexity and to support and improve business operations, as well as supporting the problem-solving and decision-making activities of managers.
It transforms Data into Information
Any information system performs four main functions:
data input - recording information data storage/retrieval - keeping information data processing - transforming information data output - displaying/presenting information
Functions of an Information System
Benefits of an Information SystemA good information system ensures:-
the right information to the right degree of accuracy when it is required in the right format/layout to the right people in the most efficient way possible
Systems development and the SDLC The need to build new information systems or
change existing ones comes about because:• there are problems in the way in which
existing systems operate; or• changes in circumstances create
opportunities to improve things by doing them differently; or
• there are external requirements or pressures, e.g. new government legislation
The Systems Development Life CycleThe SDLC provides: a systematic and orderly approach to solving business
problems a means of managing, directing, monitoring and
controlling the process of system building, including:
• a description of the process - steps to be followed
• deliverables - reports/programs/documentation/etc
• milestones - dates of completion of steps or deliverables
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Systems Development Phases
Analysis
Design
Implementation
Review
Maintenance
Quality
Documentation
Ethics
Project Management
Analysts RoleInitiation
Systems DevelopmentActivities involved in building computer-
based information systems are:- identifying problems analysing and describing information and
processing needs designing solutions to meet those needs acquiring/building new systems implementing new systems maintaining information systems
Data GatheringThe data gathered should include: system description - how things work or should
work system problems - what is wrong or needs
improvement opportunities - identifying scope for innovation
or new ways of doing things what is technically possible what constraints exist
Data gathering techniques
Interviews
Questionnaires
Observation
Reports
System Documentation
Modelling Why do we do it?
• Communication with ourselves
• Communication with others
How do we do it?• informal techniques
• formal techniques
How effective is it?• different techniques for different purposes
• eg. a road map, an organisation chart, a data flow diagram
Process modelling processes are the “action” part of
businesses process modelling graphically represents
the processes which act on data to • capture• manipulate• store• distribute
Process modelling principal techniques
• functional decomposition• data flow diagrams
associated techniques for modelling the details of low-level processes• structured English• decision tables and decision trees
Data flow diagrams (DFDs) model the flow of data into, through, and
out of an information system represent an information system as a
network of communicating processes• show the processes that change or transform
data• show the movement of data between
processes
18
2
calculateprice
loan application
Products
Suppliers
• process
• data flow
• data store
• source/sink
Components of data flow diagrams
any "real" system is too large to represent as a single data flow diagram
the solution is to decompose the system into a hierarchy of levels of processing
the process model of the system then consists of a set of levelled data flow diagrams
levelling of DFDs improves their readability and usefulness as a communication tool
Levelling Data Flow Diagrams
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Levelling DFDs
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3
1.1
1.2
Context diagram
Level zero diagram
Diagram 1 (at level 1)
Data flow diagrams may focus on either:
the “physical” view of the system’s processing
OR the “logical” view of the system’s
processing
Logical and physical DFDs
the data dictionary is a database or repository of information about objects identified during systems development
every object (and each of its components) must have a definition in the data dictionary
the data dictionary is a major source of documentation about the information system
Data Dictionary
the processing that occurs within the bottom level (primitive) processes in DFDs needs to be defined
detailed process descriptions are also known as minispecs
detailed process descriptions form part of the data dictionary: they define the contents of primitive processese.g. Structured English, decision tables, decision trees
Detailed Process Definitions
System designThe main objectives of the design phase are: to provide alternative design solutions to assist in the selection of a design solution to acquire the necessary hardware and software to design and integrate the various physical
system components .. interfaces, security controls, files/databases, etc ...
Systems design features
Design features that lead to more correct systems that are easier to maintain and modify: • Small module size .. easier to write and test, and they are
less likely to affected by change• Modular independence (coupling) .. the less the inside of
one module depends upon another, the easier it will be to test and maintain
• Modular strength (cohesion) .. measures the strength of association of elements within a module
• “black box” characteristics
Documentation• Not necessarily a piece of paper.• Any permanent medium used to communicate to other people
can be classed as documentation• Product and documentation should be developed at the same
time• DOCUMENTATION IS PART OF THE PRODUCT
Documentation is communication:• the objective is to:
• create a specific effect • on particular readers • who want specific information, • have particular characteristics and • will read under particular circumstances.
Presentations person to person communication high credibility single purpose relatively short duration a once-only event no permanent record
Using presentations in systems development reporting an important event or milestone sharing knowledge with your peers responding to a request for information gaining immediate feedback on a proposal requesting approval influencing the audience demonstrating an operational feature
systems development is a team effort teams are organised on a project basis team membership can include:
IT managers, systems analysts, users, business managers, programmers, and other specialists at various points in the project
Teams in systems development
Project manager - manages the project Analysts/designers - the architects who decide
how the system will look and work Programmers/database/network designers - the
builders who make and put together the system components
Operations/systems administration/data communications - the operational people who look after the technology infrastructure to make the system run
Computing People in the SDLC
Senior managers - who decide what the organisation’s needs and priorities are and allocate resources accordingly
Middle managers - who decide how their part of the organisation runs, allocate resources accordingly and advise or seek support from senior management when necessary
End users (operational staff) - who do the work
Business People in the SDLC
The Role of the Systems Analyst to understand the business’s information needs
• what information is needed?• for whom?• in what form?• when?
to describe the business’s information flows to identify problems and opportunities to suggest possible system solutions
Project management: why is it needed? the number of people involved the number of tasks to be done the extent of the interaction between the
tasks and people the complexity of the interactions between
the tasks and people
Basic process of project management
• Select systems development methodology• Plan the project tasks• Estimate the resources and time required to complete
individual phases of the project• Staff the project team• Organise and schedule the project effort(tasks/time/
people/technical resources) and therefore cost• Control the project development (directing the team,
controlling progress, replan, restaff, .... )
Quality in systems development various definitions e.g.
Ability to satisfy stated/implied needs the cost of detecting and correcting errors
rises greatly during the SDLC must be embedded in the systems development
process: product and process implementing quality: e.g. standards, technical
reviews
Types of Information Systems There is a range of information systems to serve
the varied needs of users:• Transaction processing systems • Electronic commerce• Process control systems • Management support systems: Management information
systems, Decision support systems, Executive information systems
• Knowledge-based systems: Expert systems, Neural networks, Robotics
• Multimedia systems• Office automation systems • Geographical information systems
each type of system has its own literature, technology, specialist skills, etc
each type of system is allied with other disciplines
a large and ever-expanding range of specialised software is available for these types of systems
each type of system requires a particular set of technical skills to develop them
different types of system tend to have different types of key users involved in their development
Types of Information Systems