Objectives: Introduction Over View of System Analysis and Design

A DFD also known as a bubble chart has the purpose of clarifying system requirements and identifying major transformations that will become programs in system design. So it is the starting point of the design phase that functionally decompose the requirements specifications down to the lowest level of detail. A DFD consists of a series of bubbles joined bylines. The bubbles represent data transformations and the lines represent data flows in the system. The system takes orders from the customer bookstore, library, etc, checks them against an index (file) listing the books available, verifies customer credit through a credit information file, and authorizes, shipment with an invoice.

6.4.1.1 DFD Symbols
In the DFD, there are four symbols A square defines a source (originator) or destination of system data.
1. An arrow identifies data flow- data in motion. It is a pipeline through which information flows.
2. A circle or a bubble (some people use an oval bubble) represents a process that transforms incoming data flows) into outgoing data flows.
3. An open rectangle is a data store- data at rest, or a temporary repository of data. Source Process Data Store

Note that a DFD describes what data flow (logical) rather than how they are processed so it does not depend on hardware, software, data structure, or the organization. The key question that we are trying to answer is What major transformations must occur for input to be correctly transformed into output Elaborate on the logical functions of the system. first, incoming orders are checked for correct book titles, author’s names and other information and their batched with other book orders from the same bookstore to determine how many copies can be shipped through the warehouse. Also, the credit status of each bookstore is checked before shipment is authorized. Each shipment has a shipping notice detailing the kind and number of books shipped. This is compared to the original order received (by mail or phone) to ascertain its accuracy. The details of the order are normally available in a special file or a data store, called bookstore orders Following order verification and credit check, a clerk batches the order by assembling all the book titles ordered by the bookstore. The batched order is sent to the warehouse with authorization to pack and ship the books to the customer. Further expansion of the DFD focuses on the steps taken in billing the bookstore. As you can tell by now, each process summarizes a lot of information and can be exploded into several lower-level detailed DFDs. This is often necessary to make sure that a complete documentation of the data flow is available for further reference.

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