Modules and modularization criteria

Modules and modularization criteria

1. Modules and modularization criteria R.Uma Selvi Assistant Professor, Department of Computer Applocations , V.V.Vanniaperumal College for Women(Autonomous) Virudhunagar

2. Modules and modularization Criteria Architectural design has the goal of producing well-structured, modular software system. Software module can be a named entity Characteristics Modules contain instructions, processing login, and data structures. Modules can be separately compiled and stored in a library Modules can be included in a program Modules segments can be used by invoking a name and some parameters Modules can use other modules

3. Examples of modules Procedures Subroutines Functions Data abstraction groups Utility groups Concurrent processes I t allows designer to decompose system into functional units. Used to isolate machine dependencies. improve the performance of a software product Ease debugging, testing, integration etc.

4. Numerous criteria to guide the modularization of a system Depending on criteria, different system structures may result. Conventional criteria  in which each module & its submodules correspond to a processing step in the execution Data abstraction  each module hides the representation details of a major data structure. Information hiding  hides difficult or changeable design decision

5. Each structure maximize cohesion of elements in each module and minimize coupling between modules. Two version of problem modeling  data structure match the problem structure and the visible functions manipulate the data structure. Modules form a network of communicating processes where each process corresponds to a problem.

6. Goal of software design is to structure the software product so that number & complexity of interconnections between modules is minimized. Strength of coupling between two modules is influenced by  interface  type of connection  types of communication. Interface established by common control blocks, common data block are more complex than interface established by parameter lists passed between modules Modification of a common data block or control block may require modification of all routines that are coupled to that block.

7. Interface communicating by parameters, modules can be modified without having to modify the routines that use the modified modules. Communication between module involves passing of data, passing elements of control etc. Degree of coupling is lowest for data communication  high for control communication  highest for modules that modify other modules. Coupling ranked on strongest(least desirable) to weakest (most desirable).

8. Types of Coupling Content Coupling Common Coupling Control Coupling Stamp Coupling Data Coupling

9. Content Coupling  Content coupling occurs when one module modified local data values or instructions in another module Common Coupling  Modules are bound together by global data structures. Control Coupling  Control coupling involves passing control flags between modules. So that one module controls the sequence of processing steps in another module.

10. Stamp Coupling  Stamp coupling is similar to common coupling, except that global data items are shared selectively among routines that require the data Data coupling  Data coupling involves the use of parameter lists to pass data items between routines.  The most desirable form of coupling between modules is a combination of stamp and data coupling

11. Cohesion The internal cohesion of a module is measured in terms of the strength of binding of elements within the module. Types (Weakest to strongest) Coincidental Cohesion Logical Cohesion Temporal Cohesion Communication Cohesion Sequential Cohesion Functional Cohesion Informational Cohesion

12. Coincidental Cohesion  Coincidental cohesion occurs when the elements within a module have no apparent relationship to one another Logical Cohesion  Logical cohesion implies some relationship among the elements of the module Ex:  In a module that performs all input and output operations , or in a module that edit all data.

13. Temporal Cohesion  Modules with temporal cohesion exhibit many of the same disadvantages as logically bound modules. Ex: module that performs program initialization Communication Cohesion The elements of a module possessing communicational cohesion refer to the same set of input and/or output data Ex: print and punch the output file  is communicationally bound.

14. Sequential Cohesion  Sequential cohesion of elements occurs when the output of one element is the input for the next element. Functional Cohesion  Functional cohesion is a strong, and hence desirable, type of binding of elements in a module because all elements are related to the performance of a single function. Informational Cohesion  It occurs when the module contains complex data structure and several routines to manipulate the data structures