1. CS 5150 1 CS 5150 Software Engineering Lecture 13 System Architecture and Design 1

2. CS 5150 2 Administration

3. CS 5150 3 System Architecture and Design The overall design of a system: Computers and networks (e.g., monolithic, distributed) Interfaces and protocols (e.g., http, ODBC) Databases (e.g., relational, distributed) Security (e.g., smart card authentication) Operations (e.g., backup, archiving, audit trails) Software environments (e.g., languages, source control tools)

4. CS 5150 4 UML: System and Subsystem Modeling Subsystem model A grouping of elements that specifies what a part of a system should do. Component (UML definition) "A distributable piece of implementation of a system, including software code (source, binary, or executable) but also including business documents, etc., in a human system." A component can be thought of as an implementation of a subsystem.

5. CS 5150 5 UML Diagrams and Specifications For every subsystem, there is a choice of diagrams Choose the diagrams that best model the system and are clearest to everybody. In UML every diagram must have supporting specification The diagrams shows the relationships among parts of the system, but much, much more detail is needed to specify a system explicitly. For example, to describe an Applet, at the very least, the specification should include the version of the protocols to be supported at the interfaces, the options (if any), and implementation restrictions.

6. CS 5150 6 UML Notation: Component & Node orderform.java A component is a physical and replaceable part of a system that conforms to and provides the realization of a set of interfaces. Server A node is a physical element that exists at run time and represents a computational resource, e.g., a computer.

7. CS 5150 7 Components and Replaceability Components allow system to be assembled from binary replaceable elements A component is physical -- bits not concepts A component can be replaced by any other component(s) that conforms to the interfaces A component is part of a system A component provides the realization of a set of interfaces

8. CS 5150 8 Components and Classes Components represent physical things. They may live on nodes. Classes represent logical abstractions. They may be grouped into packages. Classes have attributes and operations directly. Components have operations that are reachable only through interfaces.

9. CS 5150 9 Example: Simple Web System Web server Web browser Static pages from server All interaction requires communication with server

10. CS 5150 10 UML Notation: Deployment Diagram WebBrowser PersonalComp WebServer DeptServer components

11. CS 5150 11 UML Notation: Application Programming Interface (API) API is an interface that is realized by one or more components. WebServer GetPost

12. CS 5150 12 UML Notation: Interfaces WebBrowserWebServer HTTP dependency interface realization

13. CS 5150 13 Architectural Styles An architectural style is system architecture that recurs in many different applications. See: Mary Shaw and David Garlan, Software architecture: perspectives on an emerging discipline. Prentice Hall, 1996

14. CS 5150 14 Architectural Style: Client/Server Web example: Serving static pages Firefox client Apache server The control flows in the client and the server are independent. communication between client and server follows a protocol. In a peer-to-peer architecture, the same component acts as both a client and a server.

15. CS 5150 15 System Architecture Example: Extensibility in Web Browsers Web browsers provide a flexible user interface through an extensible architecture Protocols: HTTP, WAIS, Gopher, FTP, etc., proxies Data types: helper applications, plug-ins, etc. Executable code: Server-side code, e.g., servlets, CGI JavaScript at client Java applets Style sheets: CSS, etc.

16. CS 5150 16 Web User Interface: Application Server Web browser Server-side code can configure pages, access data, validate information, etc. All interaction requires communication with server Data Server

17. CS 5150 17 Architectural Style: Three Tier Architecture Web example: Serving dynamic pages Each of the tiers can be replaced by other components that implement the same interfaces Presentation tier Application tier Database tier

18. CS 5150 18 UML Notation: Interface Diagram Apache Tomcat Browser HTTP ODBC MySQL These components might be located on a single node

19. CS 5150 19 Three tier architecture: Broadcast searching User interface service User Databases This is an example of a multicast protocol. The primary difficulty is to avoid troubles at one site degrading the entire system (e.g., every transaction cannot wait for a system to time out).

20. CS 5150 20 Web User Interface: JavaScript Data Server Web browser JavaScripts can validate information as typed Some interactions are local Server interaction constrained by web protocols Java Script html

21. CS 5150 21 UML Notation: Package A package is a general-purpose mechanism for organizing elements into groups. Note: Some authors draw packages with a different shaped box: JavaScript

22. CS 5150 22 Example: Web Browser HTTP JavaScript HTMLRender Each package represents a group of objects. WebBrowser

23. CS 5150 23 Web User Interface: Applet Any server Web server Web browser Any executable code can run on client Client can connect to any server Applets

24. CS 5150 24 Applet Interfaces WebBrowserWebServer HTTP XYZServer XYZInterface

25. CS 5150 25 Architectural Style: Pipe Example: A three-pass compiler Parser Lexical analysis Code generation Output from one subsystem is the input to the next.

26. CS 5150 26 Architectural Style: Repository Repository Input components Transactions Advantages: Flexible architecture for data-intensive systems. Disadvantages: Difficult to modify repository since all other components are coupled to it.

27. CS 5150 27 Architectural Style: Repository with Storage Access Layer Data Store Input components Transactions Advantages: Data Store subsystem can be changed without modifying any component except the Storage Access. Storage Access This is sometimes called a "glue" layer Repository

28. CS 5150 28 Examples of Systems Architecture for Distributed Data: Replication Replication Several copies of the data are held in different locations. Mirror: Complete data set is replicated Cache: Dynamic set of data is replicated (e.g., most recently used) With replicated data, the biggest problems are concurrency and consistency.

29. CS 5150 29 Examples of Systems Architecture for Distributed Data: Distributed Caches.edu server cornell.edu server cs.cornell.edu server First attempt to resolve www.cs.cornell.edu 1 2 3 The Domain Name System

30. CS 5150 30 Examples of Systems Architecture for Distributed Data: Distributed Caches.edu server cornell.edu server cs.cornell.edu server Better method 3 1 almaden.ibm.com cornell.edu ece.cmu.edu ibm.com acm.org.edu 2 Local cache local DNS server The Domain Name System

31. CS 5150 31 Examples of Systems Architecture for Distributed Data: Distributed Caches For details of the actual protocol read: Paul Mockapetris, "Domain Names - Implementation and Specification". IETF Network Working Group, Request for Comments: 1035, November 1987. http://www.ietf.org/rfc/rfc1035.txt?number=1035 The Domain Name System

32. CS 5150 32 Examples of Systems Architecture for Distributed Data: Intermittent Connectivity This is an example of an epidemic protocol. Such protocols are especially useful in networks with intermittent connectivity, e.g., mobile computing. The biggest problem is ensuring that the data is distributed effectively. Example: Usenet