The Haystack Service Model Architecture

 

The bulk of functionality within Haystack is implemented by objects in the Haystack Service Model (HSM). Abstractly, Haystack can be viewed as standard three-tiered architecture consisting of three different layers, a user interface layer (the client), a server/service layer, and a database. Figure  represented the layers (and components within the layers) graphically.

This chapter primarily concerns itself with components of the service layer. The Haystack service layer consists of a number of services and the Haystack Data Model (HDM) objects running within one HaystackRootServer.

  
Figure: Abstract inter-service communication model

Figure  illustrates some of the relationships between services in Haystack. As stated previously, services run within the context of one HaystackRootServer. There are services that provide interfaces between the user and the indexing and archiving subsystems. There are services that provide utility functions for other services. For example, a name service allows for communication between other services, and a resource control service provides the mechanism for the locking of arbitrary named resources. There are services within the HaystackRootServer that ``listen'' for changes in the HDM. When those changes happen, the services are notified and they act upon the data.

• Service Architecture
  • Service Types
• The HaystackRootServer
  • The HsService Class
  • The HsNameService
    • Service Naming
• The Basic Services
  • The HsObjectCreatorService
    • Future Improvements
  • The HsDispatcher Service
    • The StarGraph Class
    • The HDM Event Model
  • The HsConfigService
    • Future Improvements
  • The HsResourceControlService
    • Future Improvements
  • The HsPersistentObjectService
    • Future Improvements
  • The HsCache Service
  • Other Base Services
    • The HsDebug, HsMessage, and HsError Services
• The Interface Services
  • The Middleman
  • The HsCommandAPI Service
    • The Command Class
    • Future Improvements
  • The HsCommunicator Service
    • Future Improvements
  • The HsCommandLine Service
• Event Driven Services
• Data manipulation Services
  • The HsArchive Service
  • The HsIndex Service
  • The HsQuery Service