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DEPARTMENT OF INFORMATION STUDIES LIS1510 Library and Archives Automation Issues Systems Analysis Andy Dawson Department of Information Studies, UCL (University of Malta 2010) Andy Dawson DEPARTMENT OF INFORMATION STUDIES What we will be looking at today • • • • • • The lifecycle concept The need for good analysis Describing the system Identifying the needs Practical exercise – process modelling Second coursework issued Andy Dawson DEPARTMENT OF INFORMATION STUDIES The system life cycle (from yesterday) • • • • Analysis Design Implementation Evaluation • Decay • Replacement Andy Dawson DEPARTMENT OF INFORMATION STUDIES The systems development lifecycle • • • • • • • • Strategic study Feasibility study Physical systems analysis Logical systems definition Logical systems design Physical systems design Implementation Maintenance Andy Dawson DEPARTMENT OF INFORMATION STUDIES Or more simply • • • • (Requirements) analysis Design Implementation Maintenance Andy Dawson DEPARTMENT OF INFORMATION STUDIES The PARIS model • • • • • Plan Ask Record Interpret Specify Andy Dawson DEPARTMENT OF INFORMATION STUDIES As we said yesterday... • • • • • • Why do so many systems seem to “fail”? Misapprehension Miscommunication Misinterpretation Misidentification Misrepresentation Andy Dawson DEPARTMENT OF INFORMATION STUDIES The role of Systems Analysis • Systems analysis allows/helps us to: – identify systems – break them down – make them work (better) • Good systems analysis helps organisations to succeed • Necessary precursor to proper system selection Andy Dawson DEPARTMENT OF INFORMATION STUDIES Requirements Analysis • • • • Identify elements Model elements Verify Importance of Conceptual Modelling Independence from physical implementation Andy Dawson DEPARTMENT OF INFORMATION STUDIES The focus of analysis • Systems tend to be Data-based or Process-based (transactional) • Transactions deal with transformations of data, input and output • Therefore we need to identify & develop transactions and data, and their interaction with the environment, to analyse a system Andy Dawson DEPARTMENT OF INFORMATION STUDIES How do we do this? • A process of expansion & contraction – Decomposition – Synthesis • Identifying and relating static & dynamic elements – Facts – Processes Andy Dawson DEPARTMENT OF INFORMATION STUDIES The value of models • Why do we model? – To improve clarity and accessibility – To show different relational aspects of the system – To help understanding • Different types of model – Data-based & Process-based – Varieties of model – Completeness of view Andy Dawson DEPARTMENT OF INFORMATION STUDIES Process modelling – The data flow diagram • Basic process modelling tool – full-scale analysis involves multiple models – different tools are used for data modelling etc • Top-down approach • Valuable for describing – current physical system – logical/desired system • Helps us to grasp system as a whole Andy Dawson DEPARTMENT OF INFORMATION STUDIES Key elements and considerations • Relationship to other models • Components – Sources/sinks (external entities) – Processes – Data stores – Data flows Andy Dawson DEPARTMENT OF INFORMATION STUDIES Symbology/notation • Importance of notation • Data flows between sources/sinks/stores via processes which transform the data • SSADM notation Andy Dawson DEPARTMENT OF INFORMATION STUDIES SSADM context diagram Andy Dawson DEPARTMENT OF INFORMATION STUDIES SSADM notation - first level DFD Andy Dawson DEPARTMENT OF INFORMATION STUDIES SSADM notation - second level DFD Andy Dawson DEPARTMENT OF INFORMATION STUDIES Naming • • • • • • Importance of naming Sources/sinks: generic descriptive Stores: simple descriptive Processes: “imperative action” concept Flows: what is tranferred Avoid ambiguity Andy Dawson DEPARTMENT OF INFORMATION STUDIES Hierarchies • Concept of levelling – Top-down decomposition – Practical levelling • Balancing – Ensure all inputs and outputs balance (match) across the levels of the hierarchy Andy Dawson DEPARTMENT OF INFORMATION STUDIES Referencing/numbering • Basic principles – Decimal heirarchies • • • • • • Lower case lettering for entities Mn/Dn stores Stores within processes Single/double flow lines and direction Multiple sources/sinks/stores Process locations/roles (physical) Andy Dawson DEPARTMENT OF INFORMATION STUDIES Constructing data flow diagrams • Follow the top-down approach • Define boundary (context diagram) • Identify – Static components – Key processes – Flows between them • Build -expand - refine - review Andy Dawson DEPARTMENT OF INFORMATION STUDIES Refining and developing the diagram • Iterative process! • Importance of – Balancing – Naming – Controlling complexity • Document flow diagrams • Data models Andy Dawson DEPARTMENT OF INFORMATION STUDIES After the break: A brief exercise in process modelling! Andy Dawson DEPARTMENT OF INFORMATION STUDIES That’s all for today! • Second coursework • Any questions? • Tomorrow: – Wrapping up the lifecycle – Feasibility studies and operational requirements – Systems selection and installation Andy Dawson