What is the objective of modular software design?

Answer 1

Software design principles represent a set of guidelines that helps us to avoid having a bad design. The design principles are associated to Robert Martin who gathered them in "Agile Software Development: Principles, Patterns, and Practices". According to Robert Martin there are 3 important characteristics of a bad design that should be avoided: * Rigidity - It is hard to change because every change affects too many other parts of the system. * Fragility - When you make a change, unexpected parts of the system break. * Immobility - It is hard to reuse in another application because it cannot be disentangled from the current application. * Software entities like classes, modules and functions should be open for extension but closed for modifications.* High-level modules should not depend on low-level modules. Both should depend on abstractions. * Abstractions should not depend on details. Details should depend on abstractions. * Clients should not be forced to depend upon interfaces that they don't use. * A class should have only one reason to change. * Derived types must be completely substitutable for their base types. * Data design - created by transforming the analysis information model (data dictionary and ERD) into data structures required to implement the software. Part of the data design may occur in conjunction with the design of software architecture. More detailed data design occurs as each software component is designed. * Architectural design - defines the relationships among the major structural elements of the software, the "design patterns" than can be used to achieve the requirements that have been defined for the system, and the constraints that affect the way in which the architectural patterns can be applied. It is derived from the system specification, the analysis model, and the subsystem interactions defined in the analysis model (DFD). * Interface design - describes how the software elements communicate with each other, with other systems, and with human users; the data flow and control flow diagrams provide much of the necessary information required. * Component-level design - created by transforming the structural elements defined by the software architecture into procedural descriptions of software components using information obtained from the process specification (PSPEC), control specification (CSPEC), and state transition diagram (STD). These models collectively form the design model, which is represented diagrammatically as a pyramid structure with data design at the base and component level design at the pinnacle. Note that each level produces its own documentation, which collectively form the design specifications document, along with the guidelines for testing individual modules and the integration of the entire package. Algorithm description and other relevant information may be included as an appendix. In order to evaluate the quality of a design (representation) the criteria for a good design should be established. Such a design should: * exhibit good architectural structure * be modular * contain distinct representations of data, architecture, interfaces, and components (modules) * lead to data structures that are appropriate for the objects to be implemented and be drawn from recognizable design patterns * lead to components that exhibit independent functional characteristics* lead to interfaces that reduce the complexity of connections between modules and with the external environment * be derived using a reputable method that is driven by information obtained during software requirements analysis These criteria are not achieved by chance. The software design process encourages good design through the application of fundamental design principles, systematic methodology and through review.

Answer 2

It means that different tasks are separated into different methods, and even into different objects.