Overview
ISO 8807:1989 - "Information processing systems - Open Systems Interconnection - LOTOS" - defines the LOTOS (Language Of Temporal Ordering Specification) formal description technique. The standard specifies the syntax and semantics for formally describing the behaviour of distributed, concurrent information‑processing systems. LOTOS is intended for rigorous service definitions, protocol specifications and conformance tests for OSI layers (ISO 7498) and can be applied to other distributed systems (for example, telephone switching networks).
Key topics and technical requirements
- Formal syntax and lexical rules: tokenisation, identifiers, comments and specification text structure as required for compliant LOTOS specifications.
- Static and dynamic semantics: detailed definitions for meanings of data types, process definitions and behaviour expressions; includes structure of static semantics and transition‑derivation rules.
- Behavioural modelling: constructs for actions, action‑prefix, choice, parallel composition, hiding, sequential composition, enable/disable, and guarded expressions to model concurrency and interaction.
- Mathematical model: many‑sorted algebras, labelled transition systems and structured labelled transition systems used as the semantics foundation.
- Data types and standard library: algebraic data type definitions, parameterized types (strings, sets, numbers, octets) and a supplied standard library for common types.
- Flattening and reconstruction: rules for flattening LOTOS specifications and reconstructing terms to support tool processing and semantics interpretation.
- Equivalence & testing theory: treatment of behavioral equivalences such as weak bisimulation and testing equivalence, with laws and congruence rules to support verification.
- Conformance and tooling support: conformance clauses describing what it means for tools and specifications to comply with the standard.
- Informative annexes & tutorial: includes a LOTOS tutorial, syntax diagrams and informal basis for abstract data types to aid adoption and learning.
Applications and who uses it
- Protocol designers and standards engineers - to produce unambiguous OSI protocol specifications and service definitions.
- System architects and developers - for modelling behavior of concurrent/distributed systems and telephone switching networks.
- Verification and test engineers - to derive conformance tests and perform formal verification using equivalence relations and transition systems.
- Tool vendors and researchers - to implement LOTOS parsers, analyzers, model checkers and to advance formal methods research.
Related standards
- ISO 7498 (OSI reference model) - target application domain for LOTOS.
- CCITT Recommendation Z.100 / SDL - related formal description techniques used for telecommunication systems.
Using ISO 8807:1989 and LOTOS enables precise, tool‑friendly descriptions of concurrency and protocol behaviour, improving clarity, verifiability and conformance testing in distributed system design.