Top-down and Bottom-up Strategies

Top-down and Bottom-up Strategies

Transformation of a DFD into Structure Chart- Transaction Analysis

·        Break the system into suitably tractable units by means of transaction analysis

·        Convert each unit into into a good structure chart by means of transform analysis

·        Link back the separate units into overall system implementation

The transaction is identified by studying the discrete event types that drive the system. For example, with respect to railway reservation, a customer may give the following transaction stimulus:

The three transaction types here are: Check Availability (an enquiry), Reserve Ticket (booking) and Cancel Ticket (cancellation). On any given time we will get customers interested in giving any of the above transaction stimuli. In a typical situation, any one stimulus may be entered through a particular terminal. The human user would inform the system her preference by selecting a transaction type from a menu. The first step in our strategy is to identify such transaction types and draw the first level breakup of modules in the structure chart, by creating separate module to co-ordinate various transaction types. This is shown as follows:

The Main ( ) which is a over-all coordinating module, gets the information about what transaction the user prefers to do through TransChoice. The TransChoice is returned as a parameter to Main ( ). Remember, we are following our design principles faithfully in decomposing our modules. The actual details of how GetTransactionType ( ) is not relevant for Main ( ). It may for example, refresh and print a text menu and prompt the user to select a choice and return this choice to Main ( ). It will not affect any other components in our breakup, even when this module is changed later to return the same input through graphical interface instead of textual menu. The modules Transaction1 ( ), Transaction2 ( ) and Transaction3 ( ) are the coordinators of transactions one, two and three respectively. The details of these transactions are to be exploded in the next levels of abstraction.

We will continue to identify more transaction centers by drawing a navigation chart of all input screens that are needed to get various transaction stimuli from the user. These are to be factored out in the next levels of the structure chart (in exactly the same way as seen before), for all identified transaction centers.