ITU-T Z.100规范：SDL形式化描述技术

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"规范描述语言SDL，全称为Specification and Description Language，是一种国际电信联盟(ITU-T)推荐的正式描述技术，用于通信系统的设计和规范。它最初被命名为CCITT Recommendation，后更新为ITU-T Recommendation Z.100。SDL主要用于系统的行为建模，特别是通信协议的描述和分析。" SDL作为形式化描述技术(FDT)的一种，它的主要目标是提供一种精确、无歧义的语言来描述通信系统的结构和行为。通过使用SDL，开发者能够清晰地定义系统组件之间的交互，包括消息传递、状态机模型以及并发和同步机制。这使得SDL成为开发和验证复杂通信协议如61850协议等的理想工具。在SDL中，有以下几个关键概念： 1. **状态机模型**：SDL支持用状态机来表示系统的动态行为，每个状态代表系统的一种操作模式，而转换则描述了系统如何在这些状态之间移动。 2. **消息传递**：SDL允许定义消息类型和消息交换的规则，这对于理解系统中不同组件间的通信过程至关重要。 3. **并发和同步**：SDL支持多线程和并发执行，允许在模型中表示多个活动同时发生。同步机制确保了在适当的时间点进行正确的通信。 4. **数据类型和结构**：SDL提供了丰富的数据类型，包括基本类型和复合类型，可以定义复杂的数据结构以适应各种通信需求。 5. **库和子程序**：SDL支持代码重用，可以创建库和子程序，以便在不同的部分或项目中复用已定义的功能。此外，SDL还与其他标准结合使用，例如与Message Sequence Chart (MSC)配合，可以提供更直观的事件序列视图，帮助开发者更好地理解和验证系统行为。Z系列的其他推荐标准，如Z.110到Z.119，进一步扩展了SDL的应用范围，提供了如消息序列图等相关技术。 SDL的应用不仅仅局限于通信行业，它也可以用于其他需要形式化建模的领域，如嵌入式系统、分布式计算等。通过使用SDL，开发者能够更准确地捕捉系统行为，减少潜在的错误，提高软件质量，并简化测试和验证过程。规范描述语言SDL是一种强大的工具，它提供了一种形式化的方法来描述和分析通信系统的结构和行为，对于理解和实现复杂的通信协议具有重要的意义。通过学习和应用SDL，开发者可以提高其设计和实现的效率，减少由于沟通不明确导致的问题，从而提升整个项目的质量和可靠性。

4 Recommendation Z.100 (11/99)

SDL was sometimes called SDL-96, it was small change compared with the change from SDL-88 to

SDL-92. The changes were:

a) harmonizing signals with remote procedures and remote variables;

b) harmonizing channels and signal routes;

c) adding external procedures and operations;

d) allowing a block or process to be used as a system;

e) state expressions;

f) allowing packages on blocks and processes;

g) parameterless operators.

These have now been incorporated into Z.100, together with a number of other changes to produce a

version of SDL known as SDL-2000. In this Recommendation the language defined by Z.100

(03/93) with Addendum 1 to Z.100 (10/96) is still called SDL-92.

The advantages of language stability, which was maintained over the period from 1992 to 1996,

began to be outweighed by the need to update SDL to support and better match other languages that

are frequently used in combination with SDL. Also modern tools and techniques have made it

practical to generate software more directly from SDL specifications, but further significant gains

could be made by incorporating better support for this use in SDL. While SDL-2000 is largely an

upgrade of SDL-92, it was agreed that some incompatibility with SDL-92 was justified; otherwise

the resulting language would have been too large, too complex and too inconsistent. This subclause

provides information about the changes. How most SDL-92 descriptions might be systematically

transformed into SDL-2000 is given in Appendix III.

Changes have been made in a number of areas, which focus on simplification of the language, and

adjustment to new application areas:

a) adjustment of syntactical conventions to other languages with which SDL is used;

b) harmonization of the concepts of system, block and process to be based on "agent" , and

merging of the concept of signal route into the concept channel;

c) interface descriptions;

d) exception handling;

e) support for textual notation of algorithms within SDL/GR;

f) composite states;

g) replacement of the service construct with the state aggregation construct;

h) new model for data;

i) constructs to support the use of ASN.1 with SDL previously in Z.105 (03/95).

Other changes are: nested packages, direct containment of blocks and processes in blocks, out-only

parameters.

On the syntactic level, SDL-2000 is case-sensitive. Keywords are available in two spellings: all

uppercase or all lowercase. Keywords of SDL-2000 that are not keywords of SDL-92 are:

abstract, aggregation, association, break, choice, composition, continue, endexceptionhandler,

endmethod, endobject, endvalue, exception, exceptionhandler, handle, method, object,

onexception, ordered, private, protected, public, raise, value.

The following keywords of SDL-92 are not keywords in SDL-2000:

all, axioms, constant, endgenerator, endnewtype, endrefinement, endservice, error, fpar,

generator, imported, literal, map, newtype, noequal, ordering, refinement, returns, reveal,

reverse, service, signalroute, view, viewed.

Recommendation Z.100 (11/99) 5

A small number of constructs of SDL-92 are not available in SDL-2000: view expression,

generators, block substructures, channel substructures, signal refinement, axiomatic definition of

data, macro diagrams. These constructs were rarely (if ever) used, and the overhead of keeping them

in the language and tools did not justify their retention.

2 References

The following ITU-T Recommendations and other references contain provisions which, through

reference in this text, constitute provisions of this Recommendation. At the time of publication, the

editions indicated were valid. All Recommendations and other references are subject to revision; all

users of this Recommendation are therefore encouraged to investigate the possibility of applying the

most recent edition of the Recommendations and other references listed below. A list of the currently

valid ITU-T Recommendations is regularly published.

− CCITT Recommendation T.50 (1992), International Reference Alphabet (IRA) (Formerly

International Alphabet No. 5 or IA5)

−

Information technology

−

7-bit coded character set

for information interchange.

ISO/IEC 646:1991, ISO 7-bit coded character set for information interchange.

3 Definitions

The are numerous terms defined throughout this Recommendation and a list of definitions in this

clause would be a repetition of much of the text of the Recommendation. Therefore only a few key

terms are given in this clause.

3.1 agent: The term agent is used to denote a system, block or process that contains one or more

extended finite state machines.

3.2 block: A block is an agent that contains one or more concurrent blocks or processes and may

also contain an extended finite state machine that owns and handles data within the block.

3.3 body: A body is a state machine graph of an agent, procedure, composite state, or operation.

3.4 channel: A channel is a communication path between agents.

3.5 environment: The environment of the system is everything in the surroundings that

communicates with the system in an SDL-like way.

3.6 gate: A gate represents a connection point for communication with an agent type, and when

the type is instantiated it determines the connection of the agent instance with other instances.

3.7 instance: An instance is an object created when a type is instantiated.

3.8 object: The term object is used for data items that are references to values.

3.9 pid: The term pid is used for data items that are references to agents.

3.10 procedure: A procedure is an encapsulation of part of the behaviour of an agent, that is

defined in one place but may be called from several places within the agent. Other agents can call a

remote procedure.

3.11 process: A process is an agent that contains an extended finite state machine, and may

contain other processes.

3.12 signal: The primary means of communication is by signals that are output by the sending

agent and input by the receiving agent.

3.13 sort: A sort is a set of data items that have common properties.

3.14 state: An extended finite state machine of an agent is in a state if it is waiting for a stimulus.

6 Recommendation Z.100 (11/99)

3.15 stimulus: A stimulus is an event that can cause an agent that is in a state to enter a transition.

3.16 system: A system is the outermost agent that communicates with the environment.

3.17 timer: A timer is an object owned by an agent that causes a timer signal stimulus to occur at

a specified time.

3.18 transition: A transition is a sequence of actions an agent performs until it enters a state.

3.19 type: A type is a definition that can be used for the creation of instances, and can also be

inherited and specialized to form other types. A parameterized type is a type that has parameters.

When these parameters are given different actual parameters, different unparameterized types are

defined that when instantiated give instance with different properties.

3.20 value: The term value is used for the class of data that is accessed directly. Values can be

freely passed between agents.

4 Abbreviations

This Recommendation uses the following abbreviations:

SDL/GR Graphic Representation form of SDL

SDL/PR Textual Phrase Representation form of SDL

SDL-2000 SDL as defined by this Recommendation

SDL-92 SDL as defined by Z.100 (03/93) with Addendum 1 (10/96)

SDL-88 SDL as defined by Z.100 (1988).

5 Conventions

The text of this clause is not normative. Instead it defines the conventions used for describing SDL.

The usage of SDL in this clause is only illustrative. The metalanguages and conventions introduced

are solely introduced for the purpose of describing SDL unambigously.

5.1 SDL grammars

SDL gives a choice of two different syntactic forms to use when representing a system; a Graphic

Representation (SDL/GR), and a textual Phrase Representation (SDL/PR). As both are concrete

representations of the same SDL, they are equivalent. In particular they are both equivalent to an

abstract grammar for the corresponding concepts.

A subset of SDL/PR is common with SDL/GR. This subset is called common textual grammar.

Although SDL can be written in either SDL/PR or SDL/GR, the language has been designed with the

knowledge that SDL/PR is used infrequently for purposes such as interchanging between tools. The

common interchange format specified in Z.106 (10/96) further diminishes the use of SDL/PR. Most

users use SDL/GR.

Figure 5-1 shows the relationships between SDL/PR, SDL/GR, the concrete grammars and the

abstract grammar.

8 Recommendation Z.100 (11/99)

T1012420-99

type

instance

instantiates as

specializes as

parameterized type

definition

with some context

parameters bound is

with all context parameters

bound is

parameterizes

implied type

Figure 5-2/Z.100 −

−−

− The type concept

Definitions introduce named entities, which are either types or instances with implied types. A

definition of a type defines all properties associated with that type. An example of an instance

definition is a process definition. An example of a definition that is a type definition is a signal

definition.

A type may be instantiated in any number of instances. An instance of a particular type has all the

properties defined for that type. An example of a type is a procedure, which may be instantiated by

procedure calls.

A parameterized type is a type where some entities are represented as formal context parameters. A

formal context parameter of a type definition has a constraint. The constraints allow static analysis of

the parameterized type. Binding all the parameters of a parameterized type yields an ordinary type.

An example of a parameterized type is a parameterized signal definition where one of the sorts

conveyed by the signal is specified by a formal sort context parameter; this allows the parameter to

be of different sorts in different contexts.

An instance is defined either directly or by the instantiation of a type. An example of an instance is a

system instance, which can be defined by a system definition, or is an instantiation of a system type.

Specialization allows one type, the subtype, to be based on another type, its supertype, by adding

properties to those of the supertype or by redefining virtual properties of the supertype. A virtual

property may be constrained in order to provide for analysis of general types.

Binding all context parameters of a parameterized type yields an unparameterized type. There is no

supertype/subtype relationship between a parameterized type and the type derived from it.

NOTE − To avoid cumbersome text, the convention is used that the term instance may be omitted. For

example "a system is interpreted......." means "a system instance is interpreted...." .

5.2.2 Environment

Systems specified in SDL behave according to the stimuli exchanged with the external world. This

external world is called the environment of the system being specified.

It is assumed that there are one or more agent instances in the environment, and therefore stimuli

flowing from the environment towards the system have associated identities of these agent instances.

These agents have pids that are distinguishable from any of the pid within the system (see 12.1.6).

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