Loosely coupled describes a resilient relationship between two or more computer systems that are exchanging data. Each end of the transaction make their requirements explicit and make few assumptions about the other end. Loosely Coupled systems are considered useful when either the source or the destination computer systems are subject to frequent changes.

Loose coupling is a design goal most sought by organizations that are implementing an Enterprise Messaging System (EMS). An Enterprise Messaging System (EMS) is a set of published Enterprise-wide standards that allows organizations to send semantically precise messages between computer systems. ...

Loose coupling is related to Web Services and Service Oriented Architecture. A web service is a collection of protocols and standards used for exchanging data between applications. ... In computing, the term Service-Oriented Architecture (SOA) expresses a software architectural concept that defines the use of services to support the requirements of software users. ...

Loose coupling can be applied to any friction-free linking enabled by open architectures. Loosely coupled services, even if they use incompatible system technologies, can be joined together on demand to create composite services, or disassembled just as easily into their functional components. Participants can establish (normatively or inceptively) a shared semantic framework to ensure messages retain a consistent meaning across participating services.

Loose coupling describes an approach where integration interfaces are developed with minimal assumptions between the sending/receiving parties, thus reducing the risk that a change in one application/module will force a change in another application/module.

Alternate definition

Loosely Coupled also describes a computer system where two or more physical processors are sharing storage disks with each other in a real time environment. The system must be designed such that the code to be shared is reentrant and that the records to be shared are protected by record locking. Record locking is the technique of preventing simultaneous access to data in a database, to prevent inconsistent results. ...

Measuring coupling

The degree of loose coupling can be measured by noting the number of changes in data elements that could occur in the sending or receiving systems and determining if the computers would still continue communicating correctly. These changes include items such as: In metadata, the term data element is an atomic unit of data that has: an identification such as a Data element name a clear Data element definition one or more Representation terms optional enumerated values In telecommunication, the term data element has the following components: A named unit of data...

1. new data elements being added to messages
2. data element order being changed
3. names or structures of data elements being changed
4. data elements being omitted

Methods for decreasing coupling

Loose coupling is dramatically enhanced when publishers of data transmit data in a flexible file format such as XML and when subscribers also publish clear definitions of how they subscribe to the messages. For example a subscriber could publish a collection the statements used to extract their information. This can be done in XML by publishing XPath expressions used in a transformation. This allows data publishers to test whether their subscribers extracts fail when the published format changes. The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. ... XPath (XML Path Language) is a terse (non-XML) syntax for addressing portions of an XML document. ...

See also

• Coupling (computer science)
• XML
• Web Services
• ISO/IEC 11179 - metadata registry specification
• Data element
• Enterprise service bus
• Enterprise Messaging System

In computer science, coupling or dependency is the degree to which each program module relies on each other module. ... The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. ... A web service is a collection of protocols and standards used for exchanging data between applications. ... ISO/IEC 11179 (formally known as the ISO/IEC 11179 Metadata Registry Standard) is a standard for representing Metadata for an organization in a Metadata Registry. ... In metadata, the term data element is an atomic unit of data that has: an identification such as a Data element name a clear Data element definition one or more Representation terms optional enumerated values In telecommunication, the term data element has the following components: A named unit of data... In computing, an enterprise service bus refers to a software architecture construct, implemented by technologies found in a category of middleware infrastructure products usually based on Web services standards, that provides foundational services for more complex service-oriented architectures via an event-driven and XML-based messaging engine (the bus). ... An Enterprise Messaging System (EMS) is a set of published Enterprise-wide standards that allows organizations to send semantically precise messages between computer systems. ...

References

• Loosely Coupled: The Missing Pieces of Web Services by Doug Kaye
• Service Oriented Architecture: A field Guild to Integrating XML and Web Services by Thomas Erl