Nearly everything in Odysseus is designed to be replaced or extended. Here are the typical ones:

• Language extensions
  • Create a new language (not only for queries, could be a DSL for anything)
  • Create a new Odysseus Script Commands (#....)
  • Create a new Logical/PQL Operator
• Processing function extensions
  • Create new datatypes
  • Create new stream object types
    • Data Handler
  • Create a new wrapper
    • Transport handler
    • Protocol handler
  • Create new functions for expressions and predicates
  • Create new aggregation functions
  • Create new operators
• Create new schedulers and scheduling strategies
• Create new meta data

Some OSGi/Eclipse basics

• Bundles
  • Aka plugin: An eclipse project
  • Each bundle has its own class loader
  • MANIFEST.MF: meta data for that bundle (name, version, imports, exports…)
  • In Odysseus: a module that encapsulates functions
• Fragment
  • A special bundle that will not exist allone but together with a host bundle
  • Same class loader as host bundle
  • Used to extend host bundle
  • We do not use this anymore, better approach is declarative services
• Declarative Services
  • OSGi way of dependency injection
  • Defined by so called components
  • Can provide functions by interfaces or use (bind/unbind) implementations by interfaces à examples later
• Feature: a feature is a collection of bundles
  • Define a set of bundles, that belong together and builds some functionality (e.g. each wrapper has its own feature)
  • An update site provides features
  • A bundle can be part of many features

• Update-site:
  • A collection of features that can be installed in Odysseus
  • On the same way, as in Eclipse („Install new software“)
  • Via command on ther server
  • Via Odysseus-Script
• Product:
  • A product is a runnable software (with an application)
  • Can be defined by bundles or features
  • We only use features to define products

OSGi Life Cycle

• Each bundle has a life cycle
• Installed: A bundle (with correct Metadata is installed)
• Resolved: All dependencies (MANIFEST) are found
• Uninstalled: removed from runtime
• Active: a bundle is activated
  • E.g. call of bundle activator
  • Remark: there is no need to start a bundle, if the bundle should only provide classes (as a library)
• Eclipse tries to resolve dependencies lazy, if this cannot be done, the bundle stays installed --> bundle cannot be used

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OSGi debugging

TODO: Check commands with apache felix console

• When an application (product) gets started with –console (as in Odysseus always), there is a console available
• ss shows all currently available bundles and their current life cycle state
• Sometimes, there are problems because dependencies are missing (INSTALLED)
• Typical problem: The dependency defined in the MANIFEST.MF was not added to any feature
• diag <id> shows the missing dependencies
• Again: Resolved is no “problem” ;-)

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• ls: shows all currently installed (declarative) services
• Unsatisfied: Some dependencies cannot be found
• Use comp <id> to determine missing dependencies

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See also some newer See also some newer slides

Setting up

This section describes how to set up Eclipse and Odysseus for development.

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