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Structuring the Program
- Objectives...................................................................................
- Software Design Methods...........................................................
- Support of Modularity.................................................................
- Separating Interface and Implementation...................................
- Separate and Independent Compilation......................................
- Libraries of Modules...................................................................
1. Objectives
How to structure large programs?
How to create large applications from small program
units?
So far we have covered requirements for simple
program units (Dealing with programming in the small).
What are the requirements for developing large
applications (programming in the large)? Mechanisms for multiple logical units Multiple programmers, and Translating design into implementation.
In many cases, the approaches that are used for small
programs do not scale up to solve large problems
We can use abstraction and modularity to assist us:
Abstraction o Allows us to concentrate on the major, important aspects of the problem, and leave the details for later o During problem analysis, we discover and invent abstractions that allow us to understand the problem Modularity o Allows us to build programming pieces that can be assembled to construct larger programs
The implementation can change without affecting the clients
3. Support of Modularity
How to support efficient modularization?
Different languages use different techniques for
building modules Class: C++, Java Package: Ada, Modula- Module: C, Pascal
Module Relationship:
A module is a server or service provider and the caller is the client.
Encapsulation:
A unit is said to encapsulate the service Combine program components that are necessary to provide the service Only make those aspects visible to clients that are required Language mechanisms provide a means for information hiding
A unit is clearly defined by two parts:
The interface describes what services are exported by the module, and imported by the client
The implementation describes the module’s internal structure that provide the service
Example: A dictionary data structure
Clients may store and retrieve pairs of the form <name, id> Operations include o Inserting a pair <"Pat", 23> o Retrieving elements by supplying the string component "Pat" o Deleting a pair based on a string Encapsulation helps to hide the implementation (array, linked list, etc.) Language Example: Built-in Types: o How float type is implemented Java: o How vector or set data types are implemented?
4. Separating Interface and Implementation
In order to use a module, we only need its interface and not its internal implementation. This clean separation contributes to the independence of the module.
Unit of compilation Order of compilation Amount of inter-module checking
6. Libraries of Modules
To control the complexity of very large programs, libraries were introduced Common modules that are used by many other modules can be grouped into standard libraries –Avoid name clashes Avoid the need to recompile when an unused part of a library changes
