1. An Active Events Model for Systems Monitoring Philip Gross Columbia University Programming Systems Lab Director: Gail Kaiser

2. 2 Motivation: Loose Coupling Want to maximize ease of distributed programming Not only should middleware deliver events… It should completely shield participants from knowledge of each other Information goes into the cloud, information comes out of the cloud

3. 3 Problem: No Event Context Consumers get data that they’re “supposed” to get Confusion and ambiguity can be major problems

4. 4 Example: Stock Trading Program Sub (MSFT > 80) // sell and cash in Event published with MSFT = 60 : ignored Event published with MSFT = 1515 : received, all shares sold Are we rich yet? Unfortunately no: was appointment with MS sales rep at 3:15pm

5. 5 We Conclude That… We need to associate semantics with event data Somehow saying “this is what I mean,” or “here’s how to interpret me” Events that explicitly indicate semantics, we call Active Events, or ActEvents They’re not just passive data containers

6. 6 Two Flavors of Information Bus Light model: information is carried by a notification service – High speed, low latency, simple behavior Heavy model: information is carried by self- transmitting software agents – Lower speed, higher latency, more sophisticated behavior

7. 7 And Two Flavors of ActEvents By reference or by value By reference: SmartEvents – Data includes structured tags – External processor maps tags to semantics By value: Gaugents – Agent ferries not just data… – But also mobile code that has semantic knowledge

8. 8 SmartEvent Implementation XML embedded in event Certain tags “exposed” for routing XML annotated to provide syntactic and semantic information FleXML (Flexible XML) enables dynamic runtime schema and semantics discovery and composition

9. 9 Initial SmartEvents Language recognition problem Validate against Schema When unknown element encountered, ask “Semantic Server” for – New schema fragment – Processing modules (Tag Processors) Tag Processors give higher-level events Supports dynamic schema composition

10. 10 Newer SmartEvents XML is described with multiple namespaces Namespaces provide direct syntactic identification Which allows lookup of Tag Processors Semantics still looked up dynamically Still supports dynamic schema composition Tag Processors can maintain state over event streams

11. 11 Two Flavors of Information Bus Light model: information is carried by a notification service – High speed, low latency, simple behavior Heavy model: information is carried by self- transmitting software agents – Lower speed, higher latency, more sophisticated behavior

12. 12 Gaugent Implementation Specialization of Worklets mobile agents Worklet Virtual Machine (WVM) installed at each participating node Java bytecode based Routing can be altered on the fly Carries data and processing code

13. 13 Gaugents Continued Worklets normally carry one junction for each WVM they plan to visit – Encapsulates computation to be performed at that location – Contains semantic information May carry jackets – Provide a mini-workflow for a particular junction, e.g. repetition, start/exit constraints, etc. – Contain manipulable routing information

14. 14 In Use: KX SmartEvents

15. 15 In Use: KX Gaugents

16. 16 Future Directions New event system Extended FleXML Web services

17. 17 Future Event System MEEP? CHIEF? Native XML Scalability, survivability, performance VPENs: Virtual Private Event Networks – Event diodes for Multi-Level Security Content-based routing, but with significant optimizations for topic-based advertisements GPL

18. 18 Conclusions Semantic annotation of events is essential for loosely coupled architectures Different solutions are appropriate for different types of information exchange We have built two implementations More experimentation needed

19. 19 Questions?

20. 20 Extended FleXML Currently one interpretation per incoming event per Metaparser Multiple consumers may need multiple interpretations Thus sets of Tag Processors may be applied to produce multiple high-level “interpretations”

21. 21 Web Services Juggernaut: Sun, IBM, Microsoft all pushing it hard Has significant implications for service interoperability projects In particular: SOAP and WSDL

22. 22 SOAP Very nice encapsulation Future probe-gauge standard? 1 2001-06-22T14:00:00-05:00 Pick up Mary at school at 2pm

23. 23 WSDL Web Services Description Language Useful for where Pub/Sub meets RPC – Types/Messages – Operation: organize into inputs and outputs – PortType: collection of Operations – Binding: mapping of PortType to e.g. SOAP – Service: set of bound PortTypes at an actual location