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Understanding Mixins and Aspects in Alfresco: Enhancing JCR Capabilities

This document explores the concept of Mixins and Aspects in Alfresco, detailing their role as metadata "plug-ins" derived from Aspect-Oriented Programming. It highlights their significance in managing cross-cutting concerns essential to JCR, such as versioning, locking, and records management for vendors. Mixins provide optional functionality, enabling the addition of properties and behavior without complicating the type hierarchy. The discussion includes requirements for querying and managing these aspects, showcasing how they can enhance data models and facilitate lifecycle management in a RESTful manner.

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Understanding Mixins and Aspects in Alfresco: Enhancing JCR Capabilities

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  1. Mixin / Aspect John Newton Alfresco Wednesday, January 28, 2009

  2. Background • Mixins or Aspects are metadata “plug-ins” • Derived from Aspect Oriented Programming • Cross-cutting concerns • Core to JCR • Exposes optional capabilities • Used for Versioning and Locking • Implements Records Mgmt for some vendors • Records aspects added when documents become records • Defines disposition information

  3. Use Cases • Optional Functionality • Example: Expose Versioning as Mixins • Systems that don’t have mixins synthesize them thru API • Avoiding Multiple Inheritence • Example: Type system exposes business data – e.g. policies • Records have metadata • Avoid type explosion thru mixins • Adding behavior • Example: control lifecycle by updating data in mixin • Very REST-like – data, not procedures

  4. Requirements • Get / Set properties that are not defined by a primary type, but are defined by an attached mixin / aspect. • Query properties that are defined in a mixin and return a target list that includes both primary type and mixin / aspect properties • Mechanism to set and remove aspects • A way to expose mixin / aspect from data dictionary

  5. Approach / Discussion • Definition • Core to model (a la JCR) • Or a special type • Get / Set properties in Mixin / Aspect • Underlying object should know whether property is available. Does not need to be modeled in core type. • Query • Mixin / Aspect is JOINed to core type • Must be explicitly listed in FROM • Add / Remove Mixin / Aspect • Same type of mechanism as Policies • Ignored by systems that do not support Aspects

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