19-09-2012, 04:19 PM
Functional Modeling & Information Flow
Functional Modelling U II.ppt (Size: 386.5 KB / Downloads: 21)
Functional Modeling
Fundamental to most of techniques used for functional modeling, is some combination of data flow diagrams and data dictionaries
Non-interactive programs, such as compilers, usually are used for computations. The functional model is the main model for such programs.
On the other hand, databases often have a trivial functional model, since their purpose is to store and organize data, not to transform it.
Function-oriented Modeling
In function-oriented modeling, a hierarchy of functions (also known as processes, transforms, transactions, bubbles, and activities) is created.
At the root of the hierarchy is the most abstract function, while the leaf nodes of the hierarchy are least abstract.
Function-oriented modeling is based on the concept of functions or processes, so they become the most important element in this approach
The functional model describes computations within a system, i.e., what happens
What is a function or a transform or process?
Each function is a sequential activity that potentially may execute concurrently with other functions
The functional model specifies the result of a computation without specifying how or when they are computed
External Entity
A producer or consumer of data
Example: person, device, system, sensor
Data must always originate from somewhere, and must always be sent to something
Process
A data transformer (changes input to output)
Example: compute taxes, determine area, format report, display graph
Data must always be process in some way to achieve system function
Data Flow Diagrams
Data flow diagrams are composed of data on the move, transformations of data into other data, sources and destinations of data, and data in static storage
Data flow diagrams show the flow of data through a system
Data Flow DiagrammingGuidelines
All icons must be labeled with meaningful names
The DFD evolves through a number of levels of detail
Always begin with a context level diagram (also called level 0)
Description of Ward’s Extensions
Data transformation
This is an example of a process, which is used to transform data values
The lowest-level functions are pure functions without side effects
A process may have side effects if it contains nonfunctional components, such as data stores or external objects