EDM Trigger Schema

What is EDM Trigger Schema?

The trigger schema adds event generation and catching capabilities for an existing EXPRESS Schema

• new reserved words:
  • TRIGGER_SCHEMA
  • TRIGGER_FUNCTION
• avoid introducing reserved words EVENT and TRIGGER as they will most likely collide with attribute names some time.
• Apart from specific extensions grammar in TRIGGER_SCHEMA is close to QUERY_SCHEMA apart from QUERY_FUNCTION 
  • Or, we might just add TRIGGER capabilities to QUERY_SCHEMA?
• The acronym is "TEX" from Trigger EXtension, and is also the file extension used for such files.

Current state of the EDM Trigger Schema

• Specification version 0.1 made, see TEX Specification

Subscribing to events from a client

The intention is that client applications can retrieve events from the EDM server. Proposal for a general approach:

• Events, here-under "trigger events" are generated 
  • from XPX code using xpxRaiseEvent(...)
  • or from EDMI code (plugins,...) using edmiRaiseEvent(..). Note that no remote version of function is available, as events are always generated on server (TODO: is this correct?)
• A client can subscribe to events. Events can be pushed (sent) or pulled (polling a queue). In either case a subscription must be active.
• To initiate subscription use function edmiRemoteSubscribeToEvents(...)
• To read events from queue use edmiRemoteGetEvents(...)
• To enable event push use edmiRemoteSetEventHandler(...)
  
• Or variations of the above

Event handlers from client can for example be:

• A web "server" receiving HTTP(s) requests - typically REST calls 
• An application like MSM providing a callback RPC function (hmm...)

Q&A:

What is aim to introduce the stuff?

Very short answer: users need to hook event handlers when certain things happen in the EDM.