1. Architecture Overview Server Database (can be on the server or separate ) Client1 Client2 Client3 HTTP  View ppt notes pages for discussion!

2. Clients Clients are thin clients Can be many kinds of user devices – PC’s, laptops, workstations, etc. Browser-based client applications (e.g. HTML, Javascript) drive these Java client applications can be used Windows/client applications also possible

3. Server Web Access Business Layer Database RMI JDBC/ODBC

4. Server (contd.) Web Access Business Layer Database Middleware in business layer (EJB’s or.NET services) Java RMI, Servlets, JSP’s etc. Database (SQL Server, Oracle, MySQL, etc.)

5. Server (contd.) Web Access Business Layer Database HTML Web Services (communicates to/from the browser) Formatting Services (formats data to/from the business layer)

6. Server (contd.) Web Access Business Layer Database Database Access Layer (formats calls unique to each DB manager) Business Logic (scheduling, conflict mgmt etc.) Transaction Management (queuing messages for each client) Admin functions Session Management (managing client sessions) Security (authentication, permissions)

7. Maintainability Localize modifications –Layered architecture Using layers as intermediaries –Semantic coherence –Generalized modules –Testability enhanced by layering

8. Usability Clients use browsers User Interface – can be off the shelf software Design Concerns –Separate user interface from the rest of the application –Model View Controller

9. Weaknesses Performance can be an issue Complexity – more layers, more classes Availability (single server) No special security considerations beyond data access