Hi,

What’s in a name? that which we call a rose
By any other name would smell as sweet
--- W Shakespeare "Romeo and Juliet"

As John MacGregor commented on today's Safety Architecture call, our discussions are occasionally marred by misunderstandings arising from the use of terminology that *seems* to be unambiguous, but actually means different things to different people, or in different contexts.

I believe that we can help to address this by compiling a common 'lexicon' of terms and definitions that we can use in ELISA discussions and publications, relating these to specific domains or contexts where necessary.

The term 'architecture', which John picked on today, for example, has at least four distinct meanings in the context of ELISA. Here are are some definitions that may be helpful:

1) Software architecture

The Software Engineering Body of Knowledge [1] includes architecture under the general heading of design, noting that "Architectural design describes how software is organized into components", while "Detailed design describes the desired behavior of these components."

It adds that a software architecture can be strictly defined as "the set of structures needed to reason about the system, which comprise software elements, relations among them, and properties of both”, but notes that it can be further subdivided into 'views' (physical, logical, process, development), focusing on different aspects of the system (distribution, functionality, concurrency, implementation).

2) System architecture

This has a very similar meaning to the term in the software context, but extends the scope to include the hardware components of a system.

IEC 61508 defines architecture as a "specific configuration of hardware and software elements in a system". ISO 26262 [3] applies the term to both hardware/software combinations and pure software elements, defining it as a "representation of the structure of the item or element that allows identification of building blocks, their boundaries and interfaces, and includes the allocation of requirements to these building blocks".

3) Safety architecture

This is more or less the same as a system architecture, but focussing only on safety.

ISO 26262 [3] defines it as the "set of elements and their interaction to fulfil the safety requirements", where an element may be a system, component (hardware or software), hardware part, or software unit.

4) CPU architecture

The term 'architecture' in discussions about the Linux kernel frequently has a different meaning again, referring to the underlying architecture of the processor (x86, ARM, MIPs, etc) in a target system, and the associated 'architecture-specific' components of the kernel.

Regards,

Paul


[1] https://www.computer.org/education/bodies-of-knowledge/software-engineering
[2] https://archive.org/details/gov.in.is.iec.61508.4.1998
[3] https://www.iso.org/obp/ui/#iso:std:iso:26262:-1:ed-2:v1:en