Shirlene Ann MedionaBSiT 3.2Mr. Danilo Rivas4 August 2009

Data-flow diagram (DFD) -is a graphical representation of the "flow" of data through an information system.

-can also be used for the visualization of data processing (structured design).

-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.

DFD symbols

Steps in developing DFD

Top-Down Approach 1. The system designer makes "a context level DFD" or Level 0, which shows the "interaction" (data flows) between "the system" (represented by one process) and "the system environment" (represented by terminators). 2. The system is "decomposed in lower-level DFD (Level 1)" into a set of "processes, data stores, and the data flows between these processes and data stores". 3. Each process is then decomposed into an "even-lower-level diagram containing its subprocesses". 4. This approach "then continues on the subsequent subprocesses", until a necessary and sufficient level of detail is reached which is called the primitive process (aka chewable in one bite).

Context Diagram -help define the scope of a project. Assess potential project benefits and risk factors.

Top-level view of IS Shows the system boundaries, external entities that interact with the

system, and major information flows between entities and the system. Example: Order system that a company uses to enter orders and apply

payments against a customer’s balanceLevel 0 and Child Diagram

Shows the system’s major processes, data flows, and data stores at a high level of abstraction

When the Context Diagram is expanded into DFD level-0, all the connections that flow into and out of process 0 needs to be retained.

Physical DFD -shows how the system will be implemented including the hardware, software, files, and people involved.

Logical DFD focuses on the business and how the business operates. -It is not concerned with how the system will be constructed.-It describes the business events that take place and the data required

and produced by each event.The logical DFD contains information about the business. The physical

DFD contains information about the computerized system.

Data Dictionaries -is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format."

-The term may have one of several closely related meanings pertaining to databases and database management systems (DBMS):

a document describing a database or collection of databases an integral component of a DBMS that is required to determine its

structure a piece of middleware that extends or supplants the native data

dictionary of a DBMS

Structured English -is the use of the English language with the syntax of structured programming.

Decision Table -are a precise yet compact way to model complicated logic. -like if-then-else and switch-case statements, associate conditions with

actions to perform.

Decision Tree -(or tree diagram) is a decision support tool that uses a tree-like graph or model of decisions and their possible consequences, including chance event outcomes, resource costs, and utility.

-commonly used in operations research, specifically in decision analysis, to help identify a strategy most likely to reach a goal.

-Another use of decision trees is as a descriptive means for calculating conditional probabilities.

Entity Relationship Diagram -is a snapshot of data structures. ERDs show entities in a database and relationships between tables within that database.