2. Specification and Modeling 2. Spec. & Modeling 2.5 Data Flow 2.6 Petri nets 2.7 Discrete event based languages 2.8 Von-Neumann languages

2.5 Data flow 2.5.1 Scope 2.5.2 Kahn process networks Def: Data flow modeling “is the process of identifying modeling and documenting how data moves around an information system. Data flow modeling examines processes, data stores, external entities, data flows”. A data flow diagram is specified by a directed graph where the nodes, called actors, represent computation and the arc represent communication channels. 2.5.2 Kahn process networks KPNs consist of nodes and edges. Nodes correspond to computations performed by some program or task. Edges imply communication via channels containing potentially infinite FIFOs. Fig. 2.40 shows a graphical representation of the KPN (p. 63). 2. Spec. & Modeling

2.5.3 Synchronous data flow SDF can best be introduced by referring to its graphical notation. Graphical representation of synchronous data flow For each execution for computation in a node is called a firing. For each firing, a number of token, representing data, is consumed and produced. Constant edge labels denote the corresponding numbers of tokens. Multi-rate SDF model Let ns be the number of tokens produced by some sender per firing, and let fr be the corresponding rate. * + 1 A B * + 1 A B D 2. Spec. & Modeling fs fr FIFO ns nr

2.6 Petri Nets 2.6.1 Introduction Petri nets model only control and control dependencies. Conditions, events and a flow relation are the key elements of Petri nets. Conditions are either satisfied or not satisfied. Events can happens. The flow relation describes the condition that must be met before events can happen and it also describes the conditions that become true if events happen. 2. Spec. & Modeling

2.7 Discrete event based language The discrete event-based model of computation is based on the idea of simulating the generation of events and the processing of event over time. 2.7.1 VHDL VHDL uses processors for modeling concurrency. 2. Spec. & Modeling

2.7.2 SystemC and SystemVerilog SystemC is a C++ class library designed to solve these problems: concurrency, time, multiple-valued logic and determinate behavior. Verilog is another hardware description language. Verilog versions 3.0 and 3.1 are also known as SystemVerilog. They include numerous extensions to Verilog 2.0. (p.99) 2. Spec. & Modeling

2.8 Von-Neumann language 2.8.1 CSP 2.8.2 ADA CSP (communicating sequential processes) is one of the first language comprising mechanisms for inter-process communication. Both processes will wait for the other process to service at the input or output statement. This is a case of rendez-vous-based, blocking or synchronous message passing. 2.8.2 ADA 2. Spec. & Modeling

2.8.3 Java 2. Spec. & Modeling