Difference between Uses and Extends


 Difference between Uses and Extends

Probably the best way to think about these diagram elements is as follows:-

"X uses Y" indicates that the task "X" has a subtask "Y"; that is, in the process of completing task "X", task "Y" will be completed at least once.

"X extends Y" indicates that "X" is a task for the same type as "Y", but "X" is a special, more specific case of doing "Y". That is, doing X is a lot like doing Y, but X has a few extra processes to it that go above and beyond the things that must be done in order to complete Y.

Comments

Post a Comment

Popular posts from this blog

What is DFD ? or What is Data Flow Diagram?

A data-flow diagram ( DFD ) is a graphical representation of the "flow" of data through an information system. DFDs can also be used for the visualization of data processing ( structured design ). On a DFD , data items flow from an external data source or an internal data store to an internal data store or an external data sink, via an internal process . A DFD provides no information about the timing or ordering of processes, or about whether processes will operate in sequence or in parallel. It is therefore quite different from a flowchart, which shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored (all of which are shown on a DFD ). ...
Read more

Symbol Used In Data Flow Diagram (DFD)

Image
Entities: can be people, departments, other companies, other systems… are called sources if they are external to the system and provide data to the system, and sinks if they are external to the system and receive information from the system Processes must have at least one input and at least one output at the primitive level (see below) are labeled with verb + object (e.g. “print invoice” or “add customer”) (e.g. in the hierarchy below, none of the processes are primitive) at the non-primitive level, are labeled more generally (e.g. “customer maintenance” or “warehouse reports”) Data stores: · can be online or “hard copy” (see notes on logical VS physical DFD’s below) · are labeled with a noun (e.g. the label “customer” indicates that information about customers is kept in that data store) · data is stored whenever there are more than one process that needs it and these processes don’t always...
Read more

Rules for Stopping the Decomposition Process in DFD

Rules for Stopping the Decomposition Process in DFD (1) when you have reduced each process to a single decision or calculation or to a single database operation;  (2) when each data store represents data about a single entity;  (3) when the system user does not care to see any more detail or when you and other analysts have documented sufficient detail to do subsequent systems development tasks;  (4) when every data flow does not need to be split further to show that different data are handled in different ways;  (5) when you believe that you have shown each business form or transaction, computer on-line display, and report as a single data flow;  (6) when you believe there is a separate process for each choice on all lowest-level menu options for the system.
Read more