- 1 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 1. Synchronous vs. asynchronous languages (1) Description of several processes in many languages non- deterministic: The order in which executable tasks are executed is not specified (may affect result). Synchronous languages: based on automata models. „Synchronous languages aim at providing high level, modular constructs, to make the design of such an automaton easier [Halbwachs]. Synchronous languages describe concurrently operating automata. „.. when automata are composed in parallel, a transition of the product is made of the "simultaneous" transitions of all of them“. Description of several processes in many languages non- deterministic: The order in which executable tasks are executed is not specified (may affect result). Synchronous languages: based on automata models. „Synchronous languages aim at providing high level, modular constructs, to make the design of such an automaton easier [Halbwachs]. Synchronous languages describe concurrently operating automata. „.. when automata are composed in parallel, a transition of the product is made of the "simultaneous" transitions of all of them“.

- 2 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Synchronous languages implicitly assume the presence of a (global) clock. Each clock tick, all inputs are considered, new outputs and states are calculated and then the transitions are made. This requires a broadcast mechanism for all parts of the model. Idealistic view of concurrency. Has the advantage of guaranteeing deterministic behavior.  StateCharts is a synchronous language. Synchronous languages implicitly assume the presence of a (global) clock. Each clock tick, all inputs are considered, new outputs and states are calculated and then the transitions are made. This requires a broadcast mechanism for all parts of the model. Idealistic view of concurrency. Has the advantage of guaranteeing deterministic behavior.  StateCharts is a synchronous language. Some general properties of languages 1. Synchronous vs. asynchronous languages (2)

- 3 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 2. Properties of processes (1) Number of processes static; dynamic (dynamically changed hardware architecture?) Nesting: –Nested declaration of processes process { process { process { }}} –or all declared at the same level process { … } process { … } process { … } Number of processes static; dynamic (dynamically changed hardware architecture?) Nesting: –Nested declaration of processes process { process { process { }}} –or all declared at the same level process { … } process { … } process { … }

- 4 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 2. Properties of processes (2) Different techniques for process creation –Elaboration in the source (c.f. ADA, below) declare process P1 … –explicit fork and join (c.f. Unix) id = fork(); –process creation calls id = create_process(P1);  StateCharts comprises a static number of processes, nested declaration of processes, and process creation through elaboration in the source. Different techniques for process creation –Elaboration in the source (c.f. ADA, below) declare process P1 … –explicit fork and join (c.f. Unix) id = fork(); –process creation calls id = create_process(P1);  StateCharts comprises a static number of processes, nested declaration of processes, and process creation through elaboration in the source.

- 5 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 3. Communication paradigms (1) Message passing –Non-blocking communication Sender does not have to wait until message has arrived; potential problem: buffer overflow Message passing –Non-blocking communication Sender does not have to wait until message has arrived; potential problem: buffer overflow … send () … receive () …

- 6 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 3. Communication paradigms (2) –Blocking communication, rendez-vous-based communication Sender will wait until receiver has received message … send () … receive () …

- 7 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 3. Communication paradigms (2) … send () … receive () … ack … –Extended rendez-vous Explicit acknowledge from receiver required. Receiver can do checking before sending acknowledgement.

- 8 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 3. Communication paradigms (4) Shared memory Variables accessible to several tasks Potential race conditions (  inconsistent results possible)  Critical sections = sections at which exclusive access to resource r (e.g. shared memory) must be guaranteed.  StateCharts uses shared memory for communication between processes. process a {.. P(S) //obtain lock.. // critical section V(S) //release lock } process b {.. P(S) //obtain lock.. // critical section V(S) //release lock } Race-free access to shared memory protected by S possible

- 9 -  P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 4. Specifying timing (1) 4 types of timing specs required [Burns, 1990]: Means for delaying processes t ? t execute Measure elapsed time Check, how much time has elapsed since last call

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Some general properties of languages 4. Specifying timing (2) Possibility to specify timeouts Stay in a certain state a maximum time.  StateCharts comprises a mechanism for specifying timeouts. Other types of timing specs not supported. Methods for specifying deadlines Not available or in separate control file. t execute

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Properties of specification languages 5. Using non-standard I/O devices - Direct access to switches, displays etc; No protection required; OS can be much faster than for operating system with protection.  No support in standard StateCharts.  No particular OS support anyhow. Direct access to switches, displays etc; No protection required; OS can be much faster than for operating system with protection.  No support in standard StateCharts.  No particular OS support anyhow.

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund SDL Language designed for specification of distributed systems. Dates back to early 70s, Formal semantics defined in the late 80s, Defined by ITU (International Telecommunication Union): Z.100 recommendation in 1980 Updates in 1984, 1988, 1992, 1996 and 1999 Language designed for specification of distributed systems. Dates back to early 70s, Formal semantics defined in the late 80s, Defined by ITU (International Telecommunication Union): Z.100 recommendation in 1980 Updates in 1984, 1988, 1992, 1996 and 1999

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund SDL Provides textual and graphical formats to please all users, Just like StateCharts, it is based on the CFSM model of computation; each FSM is called a process, However, it uses message passing instead of shared memory for communications, SDL supports operations on data. Provides textual and graphical formats to please all users, Just like StateCharts, it is based on the CFSM model of computation; each FSM is called a process, However, it uses message passing instead of shared memory for communications, SDL supports operations on data.

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund SDL-representation of FSMs/processes output input state

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Operations on data Variables can be declared locally for processes. Their type can be predefined or defined in SDL itself. SDL supports abstract data types (ADTs). Examples: Variables can be declared locally for processes. Their type can be predefined or defined in SDL itself. SDL supports abstract data types (ADTs). Examples:

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Communication among SDL-FSMs Communication between FSMs (or „processes“) is based on message-passing, assuming a potentially indefinitely large FIFO-queue. Each process fetches next entry from FIFO, checks if input enables transition, if yes: transition takes place, if no: input is ignored (exception: SAVE- mechanism). Each process fetches next entry from FIFO, checks if input enables transition, if yes: transition takes place, if no: input is ignored (exception: SAVE- mechanism).

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Process interaction diagrams Interaction between processes can be described in process interaction diagrams (special case of block diagrams). In addition to processes, these diagrams contain channels and declarations of local signals. Example: Interaction between processes can be described in process interaction diagrams (special case of block diagrams). In addition to processes, these diagrams contain channels and declarations of local signals. Example:,

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Designation of recipients 1.Through process identifiers: Example: OFFSPRING represents identifiers of processes generated dynamically. 2.Explicitly: By including the channel name. 3.Implicitly: If signal names imply channel names (B  Sw1) 1.Through process identifiers: Example: OFFSPRING represents identifiers of processes generated dynamically. 2.Explicitly: By including the channel name. 3.Implicitly: If signal names imply channel names (B  Sw1) Counter Via Sw1 Counter TO OFFSPRING

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Hierarchy in SDL Process interaction diagrams can be included in blocks. The root block is called system. Processes cannot contain other processes, unlike in StateCharts.

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Timers Timers can be declared locally. Elapsed timers put signal into queue (not necessarily processed immediately). RESET also removes timer signal from queue. Timers can be declared locally. Elapsed timers put signal into queue (not necessarily processed immediately). RESET also removes timer signal from queue.

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Additional language elements SDL includes a number of additional language elements, like procedures creation and termination of processes advanced description of data SDL includes a number of additional language elements, like procedures creation and termination of processes advanced description of data

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Application: description of network protocols

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Larger example: vending machine Machine° selling pretzels, (potato) chips, cookies, and doughnuts: accepts nickels, dime, quarters, and half- dollar coins. Not a distributed application. ° [J.M. Bergé, O. Levia, J. Roullard: High-Level System Modeling, Kluwer Academic Publishers, 1995]

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Overall view of vending machine

Decode Requests p

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund ChipHandler no yes

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Versions and tools SDL-88 SDL-92: object orientation added SDL-96 SDL-2000: Extended graphical support; processes and blocks becoming replaced by agents. Tools for connecting to MSCs (see below) Tools for connecting to UML (see below) Tools for translation to CHILL. Information: SDL-88 SDL-92: object orientation added SDL-96 SDL-2000: Extended graphical support; processes and blocks becoming replaced by agents. Tools for connecting to MSCs (see below) Tools for connecting to UML (see below) Tools for translation to CHILL. Information:

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Evaluation Excellent for distributed applications (was used to specify ISDN), Commercial tools available from SINTEF, Telelogic, Cinderella (// Not necessarily deterministic (order, in which FSMs are reading input is unknown)  no synchronous language, Implementation requires bound for the maximum length of FIFOs; may be very difficult to compute, Timer concept adequate just for soft deadlines, Limited way of using hierarchies, Limited programming language support, No description of non-functional properties. Excellent for distributed applications (was used to specify ISDN), Commercial tools available from SINTEF, Telelogic, Cinderella (// Not necessarily deterministic (order, in which FSMs are reading input is unknown)  no synchronous language, Implementation requires bound for the maximum length of FIFOs; may be very difficult to compute, Timer concept adequate just for soft deadlines, Limited way of using hierarchies, Limited programming language support, No description of non-functional properties.

 P. Marwedel, Univ. Dortmund, Informatik 12, 2005/6 Universität Dortmund Summary General language properties –Synchronous vs. asynchronous languages –Properties of processes –Communication –Timing –Access to special I/O devices SDL –Representation of processes –Communication & block diagrams –Timers and other language elements –Example: Vending machine –Versions and evaluation General language properties –Synchronous vs. asynchronous languages –Properties of processes –Communication –Timing –Access to special I/O devices SDL –Representation of processes –Communication & block diagrams –Timers and other language elements –Example: Vending machine –Versions and evaluation