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Layer (object-oriented Design)
In software object-oriented design, a layer is a group of classes that have the same set of link-time module dependencies to other modules. In other words, a layer is a group of reusable components that are reusable in similar circumstances. In programming languages, the layer distinction is often expressed as "import" dependencies between software modules. Layers are often arranged in a tree-form hierarchy, with dependency relationships as links between the layers. Dependency relationships between layers are often either inheritance, composition or aggregation relationships, but other kinds of dependencies can also be used. Layers is an architectural pattern described in many books, for example ''Pattern-Oriented Software Architecture'' [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software
Software is a set of computer programs and associated software documentation, documentation and data (computing), data. This is in contrast to Computer hardware, hardware, from which the system is built and which actually performs the work. At the low level language, lowest programming level, executable code consists of Machine code, machine language instructions supported by an individual Microprocessor, processor—typically a central processing unit (CPU) or a graphics processing unit (GPU). Machine language consists of groups of Binary number, binary values signifying Instruction set architecture, processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user. An instruction System call, may also invoke one of many Input/output, input or output operations, for example displaying some text on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inheritance (computer Science)
In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object ( prototype-based inheritance) or class ( class-based inheritance), retaining similar implementation. Also defined as deriving new classes ( sub classes) from existing ones such as super class or base class and then forming them into a hierarchy of classes. In most class-based object-oriented languages, an object created through inheritance, a "child object", acquires all the properties and behaviors of the "parent object" , with the exception of: constructors, destructor, overloaded operators and friend functions of the base class. Inheritance allows programmers to create classes that are built upon existing classes, to specify a new implementation while maintaining the same behaviors ( realizing an interface), to reuse code and to independently extend original software via public classes and interfaces. The relationships of objects or classes through inheritance give ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shearing Layers
Shearing layers is a concept coined by architect Frank Duffy, which was later elaborated by Stewart Brand in his book, '' How Buildings Learn: What Happens After They're Built'' (Brand, 1994), and refers to buildings as composed of several layers of change. The concept has been adopted by a number of technology vendors to also describe the different layers of systems within an organisation. Description The shearing layers concept views buildings as a set of components that evolve in different timescales; Frank Duffy summarized this view in his phrase: "Our basic argument is that there isn't any such thing as a building. A building properly conceived is several layers of longevity of built components" (quoted in (Brand, 1994)). The work of Duffy and DEGW identified four shearing layers (Duffy, 1992): * Shell – the traditional structure of the building that might last for 30-50 years. * Services – cabling, plumbing, aircon that needs replacing every 15 years. * Scenery – layo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multitier Architecture
In software engineering, multitier architecture (often referred to as ''n''-tier architecture) is a client–server architecture in which presentation, application processing and data management functions are physically separated. The most widespread use of multitier architecture is the three-tier architecture. ''N''-tier application architecture provides a model by which developers can create flexible and reusable applications. By segregating an application into tiers, developers acquire the option of modifying or adding a specific tier, instead of reworking the entire application. A three-tier architecture is typically composed of a ''presentation'' tier, a ''logic'' tier, and a ''data'' tier. While the concepts of layer and tier are often used interchangeably, one fairly common point of view is that there is indeed a difference. This view holds that a ''layer'' is a logical structuring mechanism for the conceptual elements that make up the software solution, while a ''tier'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abstraction Layer
In computing, an abstraction layer or abstraction level is a way of hiding the working details of a subsystem. Examples of software models that use layers of abstraction include the OSI model for network protocols, OpenGL, and other graphics libraries, which allow the separation of concerns to facilitate interoperability and platform independence. Another example is Media Transfer Protocol, which allows shared access and requires no common file system support but restricts user control compared to mass storage with block-level access. In computer science, an abstraction layer is a generalization of a conceptual model or algorithm, away from any specific implementation. These generalizations arise from broad similarities that are best encapsulated by models that express similarities present in various specific implementations. The simplification provided by a good abstraction layer allows for easy reuse by distilling a useful concept or design pattern so that situations, where ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Architectural Pattern (computer Science)
An architectural pattern is a general, reusable solution to a commonly occurring problem in software architecture within a given context. The architectural patterns address various issues in software engineering, such as computer hardware performance limitations, high availability and minimization of a business risk. Some architectural patterns have been implemented within software frameworks. The use of the word "pattern" in the software industry was influenced by similar concepts as expressed in traditional architecture, such as Christopher Alexander's '' A Pattern Language'' (1977) which discussed the practice in terms of establishing a pattern lexicon, prompting the practitioners of computer science to contemplate their own design lexicon. Usage of this metaphor within the software engineering profession became commonplace after the publication of '' Design Patterns'' (1994) by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides—now commonly known as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object Composition
In computer science, object composition and object aggregation are closely related ways to combine objects or data types into more complex ones. In conversation the distinction between composition and aggregation is often ignored. Common kinds of compositions are objects used in object-oriented programming, tagged unions, sets, sequences, and various graph structures. Object compositions relate to, but are not the same as, data structures. Object composition refers to the logical or conceptual structure of the information, not the implementation or physical data structure used to represent it. For example, a sequence differs from a set because (among other things) the order of the composed items matters for the former but not the latter. Data structures such as arrays, linked lists, hash tables, and many others can be used to implement either of them. Perhaps confusingly, some of the same terms are used for both data structures and composites. For example, "binary tree ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object Composition
In computer science, object composition and object aggregation are closely related ways to combine objects or data types into more complex ones. In conversation the distinction between composition and aggregation is often ignored. Common kinds of compositions are objects used in object-oriented programming, tagged unions, sets, sequences, and various graph structures. Object compositions relate to, but are not the same as, data structures. Object composition refers to the logical or conceptual structure of the information, not the implementation or physical data structure used to represent it. For example, a sequence differs from a set because (among other things) the order of the composed items matters for the former but not the latter. Data structures such as arrays, linked lists, hash tables, and many others can be used to implement either of them. Perhaps confusingly, some of the same terms are used for both data structures and composites. For example, "binary tree ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hierarchy
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important concept in a wide variety of fields, such as architecture, philosophy, design, mathematics, computer science, organizational theory, systems theory, systematic biology, and the social sciences (especially political philosophy). A hierarchy can link entities either directly or indirectly, and either vertically or diagonally. The only direct links in a hierarchy, insofar as they are hierarchical, are to one's immediate superior or to one of one's subordinates, although a system that is largely hierarchical can also incorporate alternative hierarchies. Hierarchical links can extend "vertically" upwards or downwards via multiple links in the same direction, following a path. All parts of the hierarchy that are not linked vertically to o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object-oriented Design
Object-oriented design (OOD) is the process of planning a Object-oriented programming, system of interacting objects for the purpose of solving a software problem. It is one approach to software design. Overview An Object (computer science), object contains Encapsulation (computer programming), encapsulated data and procedures grouped together to represent an entity. The 'object interface' defines how the Object (computer science), object can be interacted with. An object-oriented program is described by the interaction of these objects. Object-oriented design is the discipline of defining the Object (computer science), objects and their interactions to solve a problem that was identified and documented during object-oriented analysis and design, object-oriented analysis. What follows is a description of the Class-based programming, class-based subset of object-oriented design, which does not include Prototype-based programming, object prototype-based approaches where objects are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tree (data Structure)
In computer science, a tree is a widely used abstract data type that represents a hierarchical tree structure with a set of connected nodes. Each node in the tree can be connected to many children (depending on the type of tree), but must be connected to exactly one parent, except for the ''root'' node, which has no parent. These constraints mean there are no cycles or "loops" (no node can be its own ancestor), and also that each child can be treated like the root node of its own subtree, making recursion a useful technique for tree traversal. In contrast to linear data structures, many trees cannot be represented by relationships between neighboring nodes in a single straight line. Binary trees are a commonly used type, which constrain the number of children for each parent to exactly two. When the order of the children is specified, this data structure corresponds to an ordered tree in graph theory. A value or pointer to other data may be associated with every node in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reusability
In computer science and software engineering, reusability is the use of existing ''assets'' in some form within the software product development process; these ''assets'' are products and by-products of the software development life cycle and include code, software components, test suites, designs and documentation. The opposite concept of ''reusability'' is leverage, which modifies existing assets as needed to meet specific system requirements. Because reuse implies the creation of a , it is preferred over leverage. Subroutines or functions are the simplest form of reuse. A chunk of code is regularly organized using modules or namespaces into layers. Proponents claim that objects and software components offer a more advanced form of reusability, although it has been tough to objectively measure and define levels or scores of reusability. The ability to reuse relies in an essential way on the ability to build larger things from smaller parts, and being able to identify commona ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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