Presentation on theme: "Logical DFM 1 Logical DFDs Objective – To capture the essence of the current system. Start with for totally new systems or where existing system is highly."— Presentation transcript:
Logical DFM 1 Logical DFDs Objective – To capture the essence of the current system. Start with for totally new systems or where existing system is highly informa Save time by going straight to the Logical DFD if the current system is simple Can be difficult Users often more comfortable with the Current Physical DFD first
Logical DFM 2 Purpose of Logicalisation To identify problems within the current system – duplication of function and information – organisational, technological or geographic constraints To understand the basic functionality of the current system To establish the boundaries of the investigation more closely To force a switch in concentration from the real world view to the essential logical view To act as a basis for the specification of the required system.
Logical DFM 3 Determine Main Logical DFD Data Stores from LDS entities Each Logical DFD Data Store is made up of one or more Entities Group entities together in functionally related areas to form data stores e.g. Logical data store D2 Payments is made up of the Payment and Allocated Payment entities Can be done by circling groups of entities on the LDS diagram
Logical DFM 5 Replace Current Physical Data Stores with Logical Data Stores Replacement should consider opportunities for re-organising data Break up large physical data stores such as general purpose document or correspondence files Look for separate data stores containing the same data items M1 Employee M7 Name Index D1 Employee& by Personnel No.Name Index to Personnel No. D1 Stock M2 Stock List D1 Stock & combined into combined into
Logical DFM 6 Logical/Physical Data Store Cross-Reference Often get considerable duplication of data in physical system STORE I/D CURRENT PHYSICAL DATA STORELOGICAL DATA STORE M1 M2 T1(M) M2/1 T2/1(M) M5/1 Booking Sheets Driver Instructions Booking Requests Vehicle Bookings Diary Confirmed Bookings Empty Vehicles Log D3 Bookings M6/2Invoices FileD2 Payments M2/2 M6/1 Local Customer List Customer File D1 Customers M4/1Driver/Agency RegisterD5 Drivers M3/1Vehicle History CardsD4 Vehicles
Logical DFM 7 Exclude organisational and geographical considerations Remove location names from Process boxes Remove surplus references from process names and dataflow labels – all references to current forms, programs, files etc NB Only keep if new system will retain them Resulting set of logical DFDs is at the lowest level – but may not be partitioned logically at higher levels Regroup Processes on a Logical Basis 2 Warehouse Pick And Assemble
Logical DFM 8 Check for Errors and Inconsistencies Ensure that all activities essential to the system are represented Check that all dataflows at the top level are shown at lower levels Check that all lowest level dataflows are labelled Check that all data stores and processes have both inputs and outputs Walkthrough the diagram and satisfy yourself that it is correct before presenting to peers and users
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