PSXML
AUTHOR
David Hinkes
PURPOSE
PSXML is a publish-subscribe "middleware" product which harnesses the power
of XML & XPath.
MOTIVATION
There are many data distribution products ("middleware") available, however
PSXML addresses several problems with existing solutions:
* There exists a plethora of RPC based packages, however few offer a
native and intuitive-to-use publish/subscribe (observer pattern) capability.
* Most Publish/Subscribe "middlware" products deal poorly with the client data
being distributed. Most products fall into one of the following two
categories:
- Blindly passes around binary blobs and has no understanding of the message
payloads. This often creates more error-prone work for clients as they are
required to serialize thier objects manually. This category includes MTM,
JMS, et al.
- Makes use of a propreitary message specification format (meta-language),
such as IDL. This works well, but usaly requires auto-generated code.
Examples include NDDS, CORBA, ICE, et al.
* Inability to subscribe based on the contents of the client data. Most
solutions make use of a "Topic" paradigm in order to discriminate between
different virtual channels of data.
* Several solutions are also tied to a specific software language. Some
examples include DRB and JMS.
PSXML takes a novel approach to implement a pub/sub software framework:
* Designed from the bottom up to provide pub/sub functionality - nothing more
* Intuitive software API
* Use of XML for client message payloads
* Client subscriptions via XPath expressions, acting as filters on the message
contents
* Support for multiple software languages
* Open source software
Given the above, only one "middleware" product provides similar functionality:
xmlblaster (http://xmlblaster.org).