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Specification and Description Language (SDL)

SDL (Specification and Description Language) is one of the specification languages. It is known to be focused on the description and unambiguous specification of the behavior of both reactive and distributed systems.

SDL can be defined as the one focused on telecommunication systems. In 2016 its current areas of the application included the real-time applications and the process control. It can be also used for representing the simulation systems without ambiguity as well as with a graphical notation.

The Specification and Description language is known to be formally complete, being used for code generation for either final targets or simulation. It covers five main aspects: communication, structure, behavior, inheritance, and data. The behavior of the mentioned components is explained by partitioning the system into different hierarchies.

Communication between the components can be performed through different gates that are connected by channels. The mentioned channels are known to be of delayed channel type. That is the reason such communication is usually asynchronous. At the same time, when the delay is set to zero, then such communication becomes synchronous.

The Specification and Description Language (SDL) solution was developed for ConceptDraw DIAGRAM users to simplify their work with an implementation language as well as building the so-called real-time systems which are involved in the parallel processing.

Having a comprehensive selection of connectors and other diagram elements, the Specification and Description Language (SDL) solution allows all the ConceptDraw DIAGRAM users to create the professionally-looking SDL diagrams as well as other SDL-related drawings.

All systems engineers, as well as many other engineers, might find the Specification and Description Language (SDL) solution truly useful in their work.

There are 2 libraries containing 71 objects in the Specification and Description Language (SDL) solution.

Design Elements — SDL Connectors

Design Elements — SDL Connectors

Design Elements — SDL Diagrams

Design Elements — SDL Diagrams


There are a few samples that you see on this page which were created in the ConceptDraw DIAGRAM application by using the Specification and Description Language (SDL) solution. Some of the solution's capabilities as well as the professional results which you can achieve are all demonstrated here on this page.

All source documents are vector graphic documents which are always available for modifying, reviewing and/or converting to many different formats, such as MS PowerPoint, PDF file, MS Visio, and many other graphic ones from the ConceptDraw Solution Park or ConceptDraw STORE. The Specification and Description Language (SDL) solution is available to all ConceptDraw DIAGRAM users to get installed and used while working in the ConceptDraw DIAGRAM diagramming and drawing software.

Example 1: SDL Architecture

This diagram was created in ConceptDraw DIAGRAM using the SDL Connectors and SDL Diagrams libraries from the solution. An experienced user spent minutes creating this sample.

This is a generic view of an SDL system, decomposing functional blocks to the lowest level of sub-block. Processes within these sub-blocks are described as finite state machines.


Example 2: SDL Diagram — State Machine

This diagram was created in ConceptDraw DIAGRAM using the SDL Connectors and SDL Diagrams libraries from the solution. An experienced user spent 25 minutes creating this sample.

Finite state machines are inherent to the design of computer programs and sequential logic circuits. They are capable of existing in a variety of 'states', depending on certain conditions - the triggers for these conditions are noted on the diagram.

Finite State Machine

Example 3: SDL Process Game

This diagram was created in ConceptDraw DIAGRAM using the SDL Connectors and SDL Diagrams libraries from the solution. An experienced user spent 10 minutes creating this sample.

You can create logical processes that govern game theory using SDL language. Users working with ConceptDraw DIAGRAM can expect solution graphics and design elements to be held to professional technical standards.

Systems Engineering

Example 4: SDL Process Monitor

This diagram was created in ConceptDraw DIAGRAM using the SDL Connectors and SDL Diagrams libraries from the solution. An experienced user spent 20 minutes creating this sample.

It's possible to create SDL language process diagrams of any complexity using this solution and ConceptDraw DIAGRAM. Aspects such as color scheme and text style can be formatted to your taste.


Example 5: Specification and Description Language Example

This diagram was created in ConceptDraw DIAGRAM using the SDL Connectors and SDL Diagrams libraries from the solution. An experienced user spent 15 minutes creating this sample.

SDL allows you to view processes within event-driven systems in isolation, determining their state and the conditions that cause them. ConceptDraw DIAGRAM makes working with Specification and Description Language a simple task.

System Design




Specification and Description Language (SDL) Solution for macOS X

Specification and Description Language (SDL) Solution for Microsoft Windows

What I Need to Get Started

Both ConceptDraw DIAGRAM diagramming and drawing software and the Specification and Description Language (SDL) solution can help creating the illustrations the technical documentation of an engineering projects you need. The Specification and Description Language (SDL) solution can be found in the Industrial Engineering area of ConceptDraw STORE application that can be downloaded from this site. Make sure that both ConceptDraw DIAGRAM and ConceptDraw STORE applications are installed on your computer before you get started.

How to install

After ConceptDraw STORE and ConceptDraw DIAGRAM are downloaded and installed, you can install the Specification and Description Language (SDL) solution from the ConceptDraw STORE.

Start Using

To make sure that you are doing it all right, use the pre-designed symbols from the stencil libraries from the solution to make your drawings look smart and professional. Also, the pre-made examples from this solution can be used as drafts so your own drawings can be based on them. Using the samples, you can always change their structures, colors and data.

Specification Description Language (SDL) Solution - Start Using

How to Create a SDL Diagram

Specification and Description Language (SDL) Diagrams

Specification and Description Language (SDL) was initially devised in the early 1970s with a specific task in mind — to describe systems that switched state rapidly and often. The need for this language was in direct retaliation to the types of system that were rising to prominence during this time, namely telecommunication systems that had become highly complex, with heavy traffic loads and real time demands. This exposed the more rigid programming languages and hardware description languages, that were unable to represent switching systems that required standardization on an international scale.

As telecommunication systems developed, so did SDL, moving from focusing solely on sequential behavior to later adding notation for architectural composition, and finally introducing concepts such as types and inheritance. By this time, SDL was a full-time object oriented language, able to be used when modeling a system graphically (SDL/GR) or textually (SDL/PR).

The basic form of an SDL diagram will involve some or all of the following components:

Structure — the hierarchy of the system, its blocks, processes and procedures.

Communication — signals with optional parameters and channels.

Behavior — processes.

Data — abstract data types.

Inheritance — describing relations and specialization.

Different systems require a different approaches to diagram composition. Here are the three main forms of SDL diagram, and a brief description of their intent:

System architecture/structure

SDL uses a hierarchical structure comprised of 4 levels.

  • System
  • Blocks
  • Processes
  • Procedures

Complete overview of a system and it 4 layers, produced with ConceptDraw DIAGRAM

Every SDL diagram is taken as a view of system, be it a simple, single process, or more complex behavior derived from the relationship between a number of blocks. The hierarchy is nested; a system can be decomposed into blocks, each block can be describes as a process, until finally you can see the procedures that make up each process.

The advantages of this style are that a system can seen at any level — information can be shown or hidden, viewed in manageable portions, and paths can be followed individually through all their sub-divisions.


When we are describing system behavior using an SDL diagram, we are regarding blocks as finite state machines (FSM). An FSM is ideal form of component for such a diagram, as it is capable of taking on multiple forms, dependent on the type of signal input.

Using ConceptDraw DIAGRAM to take a closer look at finite state machines, with textual information to facilitate understanding

The states an FSM can switch to are clearly and unambiguously shown by the process diagram that is inherent within it. This process diagram describes every input and output of an FSM, the states they change to and from, and the actions they perform depending on which state transition takes place.


There is rarely direct human contact with a system interface as described by SDL. Transistions and interactions within the system, and with the environment, are governed by signals, which already have a pre-determined cause and effect.

A set of concurrent processes, described using ConceptDraw DIAGRAM

This keeps the blocks, or FSMs, in their finite state and as separate entities to each other — it is not possible for a signal to fundamentally disrupt or change the process within an FSM, only challenge it to make a state transition.

SDL diagrams are ideal candidates for reactive and distributive systems for a number of reasons:

  • Formal and standard language, established internationally and through many fields of industry
  • Highly testable due to formalism of structure and interface
  • Graphical and symbol based, allowing for full interpretation of detail
  • Portable, scalable and open, acting independently of operating systems, processors and distribution methods.
  • Recyclable, able to apply the same processes to many different scenarios

Specification and Description Language began life a tool for telecommunication software engineers, and it remains highly tried in that field today. Indeed, Nokia have developed their own variant named TNSDL to be used exclusively with their systems. At the same time, the user base has widened, and you can find examples of their use in automotive, aviation, and medical industries.

With a track record of producing technical, standardized solutions, CS Odessa have once again furthered the abilities of their diagramming software, ConceptDraw DIAGRAM, by releasing the Specification and Description Language solution.

The solution contains one library, with all language notation professionally drawn as vector stencil graphics. ConceptDraw DIAGRAM 's 'intelligent connector' technology allows you to be dynamic with your design, with connector lines between blocks automatically plotting an unencumbered path around the page as elements are added and relocated. As is usually the case with CS Odessa solutions, the SDL solution also contains a set of pre-designed templates and samples, to provide inspiration and to show the level of hierarchical detail that is possible.

For system engineers, the Specification and Description Language solution is the only resource necessary to create clear and focused professionally drawn SDL diagrams.