1. Winter 2007SEG2101 Chapter 41 Chapter 4 SDL – Structure and Behavior

2. Winter 2007SEG2101 Chapter 42 Contents SDL – CCITT Specification and Description Language Nested blocks Process Innermost block with processes Process behavior Substructure Services SDL symbol summary

3. Winter 2007SEG2101 Chapter 43 4.1: SDL (Specification and Description Language) Purpose and scope Basic ideas of SDL http://www.telelogic.com/products/tau/languages/sdl.cfm

4. Winter 2007SEG2101 Chapter 44 Purposes of SDL To specify precisely the functional properties of a system to be constructed; To describe precisely the functional properties of a system as it has been constructed.

5. Winter 2007SEG2101 Chapter 45 Scope of SDL Can be used in different phases of the system life cycle. May be applied over a range of abstraction levels Starting from very user-oriented, moving towards the very concrete and design dependent. Not intended as an implementation language and should not be used to bind the realization. Defined as a language and not a methodology.

6. Winter 2007SEG2101 Chapter 46 Basic Ideas of SDL SDL models independent behaviors as concurrent processes. A precise and unambiguous definition of mutual dependency is the prime concern. All dependencies are modeled explicitly as signals interchange between the processes and their environments. The theoretical foundation is the theory of finite state machine. An SDL system and its environment are conceived of as a structure of blocks connected by channels.

7. Winter 2007SEG2101 Chapter 47 Basic Ideas of SDL (II) Blocks and channels may be decomposed into blocks and channels recursively until basic components, processes, are reached.

8. Winter 2007SEG2101 Chapter 48

9. Winter 2007SEG2101 Chapter 49 Basic Ideas of SDL (III) Signalroutes are the connectors between processes. Processes in the system and the environment communicate with each other by sending signals through the signalroute and channels. There is one and only one signal input queue associated with each process.

10. Winter 2007SEG2101 Chapter 410 Basic Ideas of SDL (IV) Each process consists of the input port and an extended finite state machine.

11. Winter 2007SEG2101 Chapter 411 4.2: Nested Blocks SDL conceives a system as a structure of blocks connected by channels and such blocks may again be partitioned into blocks on lower levels. SDL systems contain concurrent processes. Draw diagram to explain

12. Winter 2007SEG2101 Chapter 412 System Level The first issue is to decide where to draw the system boundary.

13. Winter 2007SEG2101 Chapter 413 Block Blocks are system components and are connected by channel.

14. Winter 2007SEG2101 Chapter 414 Channel Channels convey signals and there may be delay on transfer of a signal. Channels connected to frame symbol represents connections to environment. Channels may also be specified to have no delay and the symbol is then equivalent to the signal route symbol, I.e. the arrow heads are at the end.

15. Winter 2007SEG2101 Chapter 415 System System is represented by a frame symbol which represents the boundary of the system.

16. Winter 2007SEG2101 Chapter 416 Block Type Definition Block type symbol indicates that there is a block type definition. Both block reference and block type reference are graphical shorthands for diagrams. The reference defines the scope of the name.

17. Winter 2007SEG2101 Chapter 417 Block Set All the block instances within a block set typically have the same relationship with its surroundings. Block set is not a reference. It designates a set of block instances. A channel connected to a block set will actually represent a set of channel instances. e, C: gate

18. Winter 2007SEG2101 Chapter 418 Signal Declaration It is necessary to declare all signals so that they are visible to the processes which handle them. A note is an explanatory text embraced by /* … */. The surrounding frame containing the textual declaration is called a text symbol. There is no limit to the numbers of text symbol in a diagram.

19. Winter 2007SEG2101 Chapter 419 Signallist A signallist is a list of signals which has been given a name. If a signallist contains other signallists, the signallist names will appear in parentheses. (Fig.4.2) The signals of a channel are denoted by a list of signals (and signallist) in brackets.

20. Winter 2007SEG2101 Chapter 420 Block Nesting A singular block may be seen as a block instance where block instance specification and block type definition is combined. Singular block instances may be specified with reference to a block type omitting cardinality of block set specification. Block types may contain a connectivity graph of block instances connected by channels. At leaves there are blocks which contain processes. Block type may not contain both blocks and processes at the same time.

21. Winter 2007SEG2101 Chapter 421 Sketch of LocalStation

22. Winter 2007SEG2101 Chapter 422 Block Type LocalStation

23. Winter 2007SEG2101 Chapter 423 Correspondence between formal description and informal description

24. Winter 2007SEG2101 Chapter 424 Gate Gates are used to indicate which channels of the block types are supposed to connect to which channel connecting an instance of type. e and C Gate names are defined by the type and visible wherever the type name is visible. Gate symbols have arrows at ends and signal lists are associated with arrows. Signallists will ensure the instances of the block type are connected correctly to their surroundings.

25. Winter 2007SEG2101 Chapter 425 4.3: What is a Process? In SDL a process is an actor object executing his own actions and having his own local (data) attributes. Processes have discrete behavior. Processes interact by means of signals. Signals are discrete stimuli which are actively screened and processes by the receiver.

26. Winter 2007SEG2101 Chapter 426 Process SDL processes are described as FSMs. Process is closely related to behavior. System and block definitions concentrated on static relationships. Process descriptions concentrate on what is changing. The structure of process is what is stable when the process behaves.

27. Winter 2007SEG2101 Chapter 427 Behavior of FSM

28. Winter 2007SEG2101 Chapter 428 Description of FSM by a Process Diagram

29. Winter 2007SEG2101 Chapter 429 Form of Process Diagram In general, each state transition has the following form. In a state transition a process sits in its current state until an expected input event is received.

30. Winter 2007SEG2101 Chapter 430 4.4: Innermost Block with Processes The leaves of the block structure will contain processes.

31. Winter 2007SEG2101 Chapter 431 Sketch of Panel

32. Winter 2007SEG2101 Chapter 432 Block Panel

33. Winter 2007SEG2101 Chapter 433 Process and SignalRoute Process symbols are connected by signalroutes.

34. Winter 2007SEG2101 Chapter 434

35. Winter 2007SEG2101 Chapter 435 Block LSControl

36. Winter 2007SEG2101 Chapter 436 4.5: Process Behavior The SDL way of describing a finite state machine (FSM). Dynamic

37. Winter 2007SEG2101 Chapter 437 Process LSControl (I)

38. Winter 2007SEG2101 Chapter 438 Process LSControl (II)

39. Winter 2007SEG2101 Chapter 439 Symbols of SDL Process Diagrams A frame surrounding the process diagram page separates a process from its environment.

40. Winter 2007SEG2101 Chapter 440 Start and State Symbol There is only one start symbol for a process. *-*-

41. Winter 2007SEG2101 Chapter 441 Input and Output Symbol

42. Winter 2007SEG2101 Chapter 442 Output Destination

43. Winter 2007SEG2101 Chapter 443 Comment and Asterisk Input * means any other input than listed.

44. Winter 2007SEG2101 Chapter 444 4.8: SDL Symbol Summary

45. Winter 2007SEG2101 Chapter 445 SDL Symbol Summary (II)