PAT.Application Hosting

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	PAT	Application Hosting	Version:	0.2
	Document type:	Pattern Type	Owner:	S.A.D. Jumelet

Informational

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Description

This Pattern Type belongs to "Infrastructure Sector Business Support". Application hosting provides a set of facilities to accommodate (business) application services. Accommodation entails

the runtime environment that the applications can use
a means to expose or publish the application services' results using web protocols
the connectivity that consumers of the application's services require for access
and optionally, extra functionality to service the application services.

Authentication/authorization is optionally included in the pattern type, but should preferably be performed using the pattern Access Security, as most necessary security functions are located in this pattern.

Graphical Overview

This is the graphical representation of the infrastructure functions in this Pattern Type, plus their main relations:

(The source file of this picture can be downloaded here).

Pattern Type Composition

This pattern has the following mandatory and optional subfunctions, expressed in Building Block Types:

Icon	Function	WA	Inclusion	Rationale
	Presentation Engine	SE	mandatory	This BBT delivers an important part of the core functionality of any application hosting solution: the presentation of the application to the client. The technology used here must match those available at the client (e.g. HTTP implies browser, X Window implies X Server etc)
	Presentation Aggregation	SE	optional	When combining multiple hosted applications, Presentation Aggregation may serve to share (presentation-specific) functionality.
	Application Engine	SE	mandatory	This BBT delivers the core functionality of the pattern.
	Scheduling	MW	optional	While application hosting usually responds to client request, it may be convenient to have the application also respond to other triggers; the Scheduler BBT provides the capability for this.
	Transaction Coordination	MW	optional	When multiple instances of one business application are necessary AND the transactions that the facility must process are interdependent, then this BBT can provide the necessary coordination.
	Control Interface	SE	optional	The Application Hosting facility should preferably be managed by a centralized facility, but if this is not possible or feasible, then a means must be offered to manage the facility itself - and the Control Interface offers this means. Note that this facility is limited to the Application Hosting facility, and cannot directly manage the applications running on the Application Hosting facility.
	Message Coordination	SE	optional	If an Application Hosting facility is to be able to offer its applications the possibility to send out messages (such as e-mail), then this function acts as intermediary between the application and the message handling service

Pattern Type Neighbors

This pattern has the following mandatory and optional relations with adjacent (sub)functions, expressed in Pattern Types (PAT). Note: if the table below is empty, then there are no architecturally prescribed relations with adjacent subfunctions:

Function	Adjacency	Description
Raw Storage	optional	Should the Application Hosting facility need to offer hosted applications the ability to store unstructured data, then inclusion of this pattern is needed.
Data Management	optional	Should the Application Hosting facility need to offer hosted applications the ability to store structured data, then inclusion of this pattern is needed.
Authentication & Authorization	optional	When authentication/authorization (A&A) is needed and cannot be (fully) catered for in an Access Security pattern, then the A&A facility is necessary. Authorization can be paired with Application Hosting relatively easy, but application of authorization is more secure if it takes place earlier in the traffic stream from client to application - hence the usage of Access Security --including A&A-- is preferable.
Message Handling	optional	This facility offers the means to deliver data to applications, and/or to enable applications to send data out. It may provide asynchronous messaging (like email or XML messages), synchronous messaging (like SOAP messages over HTTP or RPC) or both.

Pattern Variants based on this type

Pattern Variant	Brief description	Owner	maturity
PAV.Application Hosting.Cloud - Internal Access Only Best Effort	Cloud - Internal Access Only Best Effort	S.A.D. Jumelet	3