Process Design Language (PDL) is a kind of in which the design is communicated precisely according to the desired of the designer. Basically, is used to specify the design of system and to extend it to logic design. Process Design Languages have been used for some time in the informal description of software and as an aid to top-down program construction.
PDL is used to express the design in a language that is as precise and unambiguous as possible without having too much detail and that can be easily converted into an implementation. This is what PDL attempts to do. It is the outer syntax of a structured programming language and also it has a vocabulary of a natural language. It can be thought of as structured English.
PDL Example :
Consider the problem of reading the record from the file. If file reading is not completed and there is no error in the record then print the information of the record otherwise print that there is an error in reading of the record. This process will continue till the whole file is completed:
Process (F_Procedure) Read file while not end-of-life if record ok then print record else prinr error else if read file end while End
To implements will have to be converted into programming language statements.
Programming Constructs :
The basic constructs of PDL are similar to those of a structured language. The following are the conditional operators and loops used in PDL.
1. Sequence Construct : It is the simplest; whereby statements are executed in the order they’re found in procedure.
2. If construct : The if construct is used to control the flow of execution down one of two or more paths, depending on the result of given condition.
3. Selection Constructs : The selection construct are used when the flow of execution may flow down two or more paths. When there are many conditions and the vales are discrete, selection constructs are used. There are two or more conditions in the selection constructs. Each condition statement is an entry point, and execution will continue from that point unless a break statement is used. The break statement causes the program to continue from the end of the selection construct. Only discrete values may be used for the conditions.
4. Repetition Constructs : The repetition construct are used when a block of code is required to be executes continually until a condition is met. This type of loop is used to execute the block of code and the condition should be true.
A variety of data structure can be defined and used in PDL such as lists, tables, scalar and integers.
Advantages of PDL :
- It can be embedded with source code, therefore easy to maintain.
- It enables declaration of data as well as procedure.
- It is the cheapest and most effective way to change program architecture,
Disadvantages of PDL :
- It is unable to express the functionality in an understandable way.
- Only notation is understandable to people with PDL.
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