The text is a product in the sense that it is an output, something that can be recorded and studied, having a certain construction that can be repres… - Michael Halliday

[... language, as an example of a semiotic system, contains all four levels of organization as follows:] First, it is transmitted physically, by sound waves traveling through the air; secondly, it is produced and received biologically, by the human brain and its associated organs of speech and hearing; thirdly it is exchanged socially, in contexts set up and defined by the social structure; and fourthly it is organized semiotically as a system of meanings

Saussure took the sign as the organizing concept for linguistic structure, using it to express the conventional nature of language in the phrase "l'arbitraire du signe". This has the effect of highlighting what is, in fact, the one point of arbitrariness in the system, namely the phonological shape of words, and hence allows the non-arbitrariness of the rest to emerge with greater clarity. An example of something that is distinctly non-arbitrary is the way different kinds of meaning in language are expressed by different kinds of grammatical structure, as appears when linguistic structure is interpreted in functional terms.

The grammatical system has … a functional input and a structural output; it provides the mechanism for different functions to be combined in one utterance