Difference between a module, library and a framework

Question

In popular programming speak, what is the difference between these terms and what are the overlaps?

Any related terms I\'m missing out?

Answer 1

Module

A module is the output of modular design, a component with various granularity.

In context of modular programming, a module is an entity expressible by the coding language introducing the programmability (typically, a programming language or a hardware description language) to the solution.

Some languages explicitly support the concept of module and provide it as a language feature. A notable early instance is Modular-2. Despite the feature, users can still specify other kinds of modules by conventions with different granularity in software design and project management, like a source file and a directory of source files. The built-in language feature does not eliminate the need of modules of different granularity, but people may use different terminology to avoid possible ambiguity with the language feature.

Some other languages do not provide specific feature named module, but users can make choices to specify parts of program as modules. For example, the C language does not have modules, but users can specify a function, a source file, a translation unit (a source file with the headers it includes) or even bunch of files as a module on demand. A module in such case can be with different forms of code: source, binary code from source or provided elsewhere with linkage compatibility guarantees, or even mixed.

The only real restriction of "module", if any, is that it should reflect to the result of some modular design, so components in a module should share some similarities to make the boundary clear. A module should usually provide some kinds of exported interface to users; it may optionally import dependencies from external program components. Some of modules can be a submodule of others.

Code management tools may utilizes the concepts related to module. For example, Git has the concept of submodule, which is essentially a versioned subdirectory of code in the repository.

Library

A library is a specialized kind of program module containing (more specifically, owning) a collection of (sub)modules to be used in some encapsulated (that is, not allowed being modified directly in later use) manner. Usually a library is designed to be reused and deployed within non-volatile storage. Typically, a library is provided as one or several on-disk files in some steady persistent formats. Such libraries are called archives, dynamic objects, packages, etc. With support of external program databases, libraries can also be identified by means other than filenames or other file-based properties. For example, CLI provides library assemblies with aid of GAC.

Framework

A framework is another specialized kind of program module which contains various pre-desinged functionality of code. A framework can be deployed in a form of one or several libraries. The difference between a framework and other kinds of modules in a program is that the former emphasizes a mostly complete, freezed but adaptive and extensible solution of some common work, so the user of the framework can focus on the domain-specific and project-specific problems instead of writing glue code to put different libraries together and to make them work fluently. However, this has a cost of design complexity throughout the whole project. Notably, many (but not all) frameworks would enforce users' code following an IoC style. As a result, it is almost impossible to put same kind but different frameworks together smoothly in an idiomatic and natural way. Using language with first-class control effects, IoC is not explicitly required in a framework. However this implies that combination of normal libraries to having functionality of a framework is easier to achieve, so there is less need to organize program modules like traditional frameworks which often undermine flexibility easily.