Model-view-adapter
Encyclopedia
Model–view–adapter or mediating-controller MVC
is an architectural pattern
and multitier architecture
, used in software engineering
. In complex computer applications that present large amounts of data to users, developers often wish to separate data (model) and user interface
(view) concerns so that changes to the user interface will not affect data handling and that the data can be reorganized without changing the user interface. MVA and traditional MVC both attempt to solve this same problem, but with two different styles of solution. Traditional MVC arranges model (e.g., data structures and storage), view (e.g., user interface), and controller (e.g., business logic) in a triangle, with model, view, and controller as vertices, so that some information flows between the model and views outside of the controller's direct control. The model–view–adapter solves this rather differently than the model–view–controller does by arranging model, adapter or mediating controller, and view linearly without any connections whatsoever directly between model and view.
the model might best be a piece table (instead of, say, a gap buffer
or a linked list
of line
s), but the user interface should present the final resting state of the edits on the file, not some direct information-overload
presentation of the piece-table's meticulous raw undo-redo deltas and incremental operations on that file since the current editing session began.
permits a wide variety of different views to indirectly access the same model either via exactly the same adapter or via the same class of adapters. For example, one underlying data-storage model and schema and technology could be accessed via a wide variety multiple different views—e.g., Qt GUI
, Microsoft
MFC GUI, GTK+
GUI, Microsoft .NET
GUI, Java Swing
GUI, Silverlight
website
, and AJAX
website—, where (unlike traditional MVC) the model is kept completely oblivious of what information flows toward these user interfaces. The adapter or class of adapters keeps the model completely oblivious that it is supporting multiple of the user interfaces and perhaps even supporting this variety concurrently. To the model, these multiple types of user interface would look like multiple instances of a generic user oblivious of type of technology.
database server
such as PostgreSQL
, Sybase
, or SQL Server
that has business logic
built into the database server
via stored procedures and that has transactions that the server may roll back or B) by an SQL database server such as MySQL
that lacks one or more of these capabilities, or C) by a nonSQL RDF
database, because the website interacts only with the mediating controller or adapter and never directly with the model.
of the USA or different nation-states internationally) may impose different codes of law, that in turn impose different business logic for the same underlying database and for the same outwardly-presented website. In this scenario, a class of various adapters or mediating controllers can represent the variations in business logic among these jurisdictions in between the same database model and the same website view.
Model-view-controller
Model–view–controller is a software architecture, currently considered an architectural pattern used in software engineering. The pattern isolates "domain logic" from the user interface , permitting independent development, testing and maintenance of each .Model View Controller...
is an architectural pattern
Architectural pattern (computer science)
An architectural pattern in software is a standard design in the field of software architecture. The concept of a software architectural pattern has a broader scope than the concept of a software design pattern...
and multitier architecture
Multitier architecture
In software engineering, multi-tier architecture is a client–server architecture in which the presentation, the application processing, and the data management are logically separate processes. For example, an application that uses middleware to service data requests between a user and a database...
, used in software engineering
Software engineering
Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...
. In complex computer applications that present large amounts of data to users, developers often wish to separate data (model) and user interface
User interface
The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...
(view) concerns so that changes to the user interface will not affect data handling and that the data can be reorganized without changing the user interface. MVA and traditional MVC both attempt to solve this same problem, but with two different styles of solution. Traditional MVC arranges model (e.g., data structures and storage), view (e.g., user interface), and controller (e.g., business logic) in a triangle, with model, view, and controller as vertices, so that some information flows between the model and views outside of the controller's direct control. The model–view–adapter solves this rather differently than the model–view–controller does by arranging model, adapter or mediating controller, and view linearly without any connections whatsoever directly between model and view.
View and model do not communicate directly
The view is completely decoupled from the model such that view and the model can interact only via the mediating controller or adapter in between the view and the model. Via this arrangement, only the adapter or mediating controller has knowledge of both the model and the view, because it is the responsibility of solely the adapter or mediating controller to adapt or mediate between the model and the view—hence the names adapter and mediator. The model and view are kept intentionally oblivious of each other. In traditional MVC, the model and view are made aware of each other, which might permit disadvantageous comingling of view (e.g., user interface) concerns into the model (e.g., database) and vice versa, when the architecture might have been better served by the schema of the database and the presentation of information in the user-interface are divorced entirely from each other and allowed to diverge from each other radically. For example in a text editorText editor
A text editor is a type of program used for editing plain text files.Text editors are often provided with operating systems or software development packages, and can be used to change configuration files and programming language source code....
the model might best be a piece table (instead of, say, a gap buffer
Gap buffer
A gap buffer In computer science is a dynamic array that allows efficient insertion and deletion operations clustered near the same location. Gap buffers are especially common in text editors, where most changes to the text occur at or near the current location of the cursor. The text is stored in...
or a linked list
Linked list
In computer science, a linked list is a data structure consisting of a group of nodes which together represent a sequence. Under the simplest form, each node is composed of a datum and a reference to the next node in the sequence; more complex variants add additional links...
of line
Line (text file)
In computing, a line is a unit of organization for text files. A line consists of a sequence of zero or more characters, usually displayed within a single horizontal sequence....
s), but the user interface should present the final resting state of the edits on the file, not some direct information-overload
Information overload
"Information overload" is a term popularized by Alvin Toffler in his bestselling 1970 book Future Shock. It refers to the difficulty a person can have understanding an issue and making decisions that can be caused by the presence of too much information...
presentation of the piece-table's meticulous raw undo-redo deltas and incremental operations on that file since the current editing session began.
Model is intentionally oblivious of views
This separation of concernsSeparation of concerns
In computer science, separation of concerns is the process of separating a computer program into distinct features that overlap in functionality as little as possible. A concern is any piece of interest or focus in a program. Typically, concerns are synonymous with features or behaviors...
permits a wide variety of different views to indirectly access the same model either via exactly the same adapter or via the same class of adapters. For example, one underlying data-storage model and schema and technology could be accessed via a wide variety multiple different views—e.g., Qt GUI
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
, Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
MFC GUI, GTK+
GTK+
GTK+ is a cross-platform widget toolkit for creating graphical user interfaces. It is licensed under the terms of the GNU LGPL, allowing both free and proprietary software to use it. It is one of the most popular toolkits for the X Window System, along with Qt.The name GTK+ originates from GTK;...
GUI, Microsoft .NET
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
GUI, Java Swing
Swing (Java)
Swing is the primary Java GUI widget toolkit. It is part of Oracle's Java Foundation Classes — an API for providing a graphical user interface for Java programs....
GUI, Silverlight
Microsoft Silverlight
Microsoft Silverlight is an application framework for writing and running rich Internet applications, with features and purposes similar to those of Adobe Flash. The run-time environment for Silverlight is available as a plug-in for web browsers running under Microsoft Windows and Mac OS X...
website
Website
A website, also written as Web site, web site, or simply site, is a collection of related web pages containing images, videos or other digital assets. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet...
, and AJAX
Ajax
- Mythology :* Ajax , son of Telamon, ruler of Salamis and a hero in the Trojan War, also known as "Ajax the Great"* Ajax the Lesser, son of Oileus, ruler of Locris and the leader of the Locrian contingent during the Trojan War.- People :...
website—, where (unlike traditional MVC) the model is kept completely oblivious of what information flows toward these user interfaces. The adapter or class of adapters keeps the model completely oblivious that it is supporting multiple of the user interfaces and perhaps even supporting this variety concurrently. To the model, these multiple types of user interface would look like multiple instances of a generic user oblivious of type of technology.
View is intentionally oblivious of models
Likewise, any one user interface can be kept intentionally oblivious of a wide variety of different models that may underlie the mediating controller or adapter. For example, the same website can be kept oblivious of the fact that it can be served by an SQLSQL
SQL is a programming language designed for managing data in relational database management systems ....
database server
Database server
A database server is a computer program that provides database services to other computer programs or computers, as defined by the client–server model. The term may also refer to a computer dedicated to running such a program...
such as PostgreSQL
PostgreSQL
PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
, Sybase
Sybase
Sybase, an SAP company, is an enterprise software and services company offering software to manage, analyze, and mobilize information, using relational databases, analytics and data warehousing solutions and mobile applications development platforms....
, or SQL Server
SQL Server
SQL Server may refer to:* Any database server that implements the Structured Query Language* Microsoft SQL Server, a relational database server from Microsoft* Sybase SQL Server, a relational database server developed by Sybase...
that has business logic
Business logic
Business logic, or domain logic, is a non-technical term generally used to describe the functional algorithms that handle information exchange between a database and a user interface.- Scope of business logic :Business logic:...
built into the database server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
via stored procedures and that has transactions that the server may roll back or B) by an SQL database server such as MySQL
MySQL
MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...
that lacks one or more of these capabilities, or C) by a nonSQL RDF
Resource Description Framework
The Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
database, because the website interacts only with the mediating controller or adapter and never directly with the model.
Multiple adaptors between the same model-view pair
Additionally, multiple adapters may be created to change the way one view presents data for a given model. For example, different governments (either among different statesU.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
of the USA or different nation-states internationally) may impose different codes of law, that in turn impose different business logic for the same underlying database and for the same outwardly-presented website. In this scenario, a class of various adapters or mediating controllers can represent the variations in business logic among these jurisdictions in between the same database model and the same website view.