1. Chapter 6: Using Middleware Textbook IT Architectures and Middleware, Second Edition Chris Britton and Peter Bye AIT 600 Jeff Schmitt October 20, 2008

2. Questions to explore ● What is middleware for? ● How do we split application functionality among the tiers? ● How do we assemble applications into a wider architecture?

3. What is middleware for? ● Transaction technology – as used in the implementation of business processes and services ● Information retrieval technology – as used to support management oversight and analysis of business performance ● Collaborative technology – for helping people work together, email, discussion forum, wiki ● Internal IT service technology – software distribution, remote system operation

6. How do we split application functionality among the tiers? ● How do we split

9. Distributed Architecture patterns ● How do we assemble applications into a wider architecture?  Middleware bus (or ring) – tightly coupled  Hub and spoke – medium coupling  Loosely coupled – as in Web Services  No plan – ad hoc – solve each crisis as it occurs

10. Middleware Bus ● Primary aim: separate presentation channels from the business services ● Advantages  Fast – network hardware and software tailored for production workload  Secure – barriers against breaking  Flexible – new channels added easily ● High-discipline architecture  strict standards for service interface, security, system management and failover

13. Hub Architecture ● Messages go through hub giving opportunities for functionality  Reouting the message  Multicasting the message (broadcast)  Reformatting or splitting the message  Adding information to the message  Perform workflow rules  Monitor message flow ● Useful in bridging networks, and in legacy systems where you cannot adapt the application

15. Hub Disadvantages ● Another link in the chain ● Another point of failure ● Potential bottleneck ● Need backup hub and failsafe software

17. Web Services Architecture ● Loosely coupled distributed system ● Dependencies between distributed programs  Protocol  Configuration  Message format  Message semantics  Session state  Security  Business process  Business object

18. Dimensions of coupling dependencies ● Technological dimension  Protocol  Configuration  Message format ● Application dimension  Message semantics  Session state ● Wider concerns  Security  Business process  Business object

19. Summary ● Communication among applications  Real-time (request and response)  Deferrable (send and forget) ● Business processes, collaboration, intelligence ● Tiers – useful concept for program design  Presentation tier – support multiple external channels – clear cut  Processing and data tier – less clear cut delineation

20. Summary ● Application coupling (loose or tight) has technical dimension and application dimension  Technical dimension – example web services  Application dimension – example complex dialog to exchange information ● Distributed architecture styles  Middleware bus architecture  Hub architecture  Web services architecture

21. Summary ● Middleware bus architecture  Tightly coupled  Best performance, resiliency and security but difficult to deploy and change ● Hub architecture  Moderately coupled  Useful when there is a need to route service requests or to multicast service requests ● Web services architecture  Loosely coupled