Services Overview

[ahansen@tridium.com]

While we are waiting for Brian's proposal, here is a general overview for our newer members.

I'd like to this to turn into a document for the outside world.  I am not the best writer, so feedback of any nature is welcome.

If you would like a meeting to discuss this, let me know soon to have it next week.  Otherwise, I will be on vacation Aug. 9 - 13.

Best,
Aaron

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oBIX XML Core Services Overview


About This Document
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This document provides an overall view of oBIX core web services.  It is intended for a general audience, and is not a technical specification. This is not an official OASIS document.


Overview
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oBIX is defining standard web services for enterprise access to data acquisition and control systems.  The core of the standard will be a foundation of common types and services applicable to horizontal issues including discovery, data access, historical trends, and alarming.  These services can be deployed in verticals domains such as HVAC, security, power management and lighting.

The core services are autonomous and have only a loosely coupled relationship to a central discovery service.  The discovery service models a system and directs clients to appropriate services for accessing data it models.


Discovery Service
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The discovery service provides a central mechanism for learning what data is available and what services can be used to manipulate it.  It is the fundamental bootstrap from which other services can be accessed.  By separating this function, other services will not need to reinvent discovery, integrators will have a central point of access to a system, and arbitrary services can be easy integrated together.

The ability to integrate arbitrary services is what makes this the most important service in oBIX.  It will give vendors and integrators the flexibility to assemble best-of-breed services for their systems.  While this sounds like fantasy, there is no technical limitation to its implementation.  Since nearly all pieces of data are addressable, one can generically convey a piece of data and it's address for any given service.  Data modeled by the discovery service may have zero or more service bindings.

The discovery service also identifies data types.  Like service bindings, any piece of data can have zero or more types and typing is not limited to data with service bindings.  For example, a piece of data can be an OPC XML data point, a BACnet XML data point, and an oBIX data point.

What the discovery service models is an implementation detail.  It can model a physical or logical system structure; or both.  It can also be used to model complex composite pieces of data.  The oBIX data service provides access to primitive data types.  If a data type is an aggregate of primitives, the discovery service could be used to model their relationship.


Data Service
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The data service allows clients to read and write the oBIX set of primitive data types.  This data could be real time control points such as actuators and sensors, or it could be vendor properties such as version number or support contact information.

oBIX provides a very small set of primitive data types.  Whether or not a number is signed or has a given number of bits are the kinds of details oBIX wants to hide from clients.  For example, oBIX will provide a single data type for all numbers and meta-data will be used to define precision, minimum values and maximum values.  Meta-data will also be used to provide a number of facets including units, enumeration ranges and documentation.

In addition to explicit client requests for data values, the data service will support data subscription.  With subscription, the client instructs the server to only notify of data changes which greatly optimizes system performance.


Historical Data Service
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Historical data is needed to understand trends within a system for optimizing performance, efficiency, and user experience.  The oBIX historical data service is used to query trend data that has been collected by the server as time stamped value samples.


Alarm Service
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The alarm service provides a normalized representation of an alarm event record.  It provides the ability to query alarms that have occurred on the server, the ability to subscribe for new alarms which are generated, and the ability to acknowledge existing alarms.