Functional view: In the 1960s, British linguists developed a system of categories based on the communicative needs of the learner and proposed a syllabus based on communicative functions. The functional view not only sees language as a linguistic system but also a means for doing things. Most of our day-to-day language use involves functional activities: offering, suggesting, advising, apologizing, etc. Therefore, learners learn a language in order to be able to do things with it. In order to perform functions, learners need to know how to combine the grammatical rules and the vocabulary to express notions that perform the functions. Examples of notions are the concept of present, past & future time, the expressions of certainty and possibility, the roles of agents, instruments within a sentence, and special relationships between people and objects.
Interactional view: the interactional view considers language to be a communicative tool, whose main use is to build up and maintain social relations between people. Therefore, learners not only need to know the grammar and vocabulary of the language but as importantly they need to know the rules for using them in a whole range of communicative contexts.
Functional Sentence Perspective (FSP): Functional Sentence Perspective (FSP) is a theory of linguistic analysis which refers to an analysis of utterances (or texts) in terms of the information they contain. The principle is that the role of each utterance part is evaluated for its semantic contribution to the whole.
Systemic-Functional Grammar has two components: systemic grammar and functional grammar. They are two inseparable parts for an integral framework of linguistic theory. Systemic grammar aims to explain the internal relations in language as a system network, or meaning potential. And this network consists of subsystems from which language users make choices. Functional grammar aims to reveal that language is a means of social interaction, based on the position that language system and the forms that make it up are inescapably determined by the uses or functions which they serve.
The Ideational Function is to convey new information, to communicate a content that is unknown to the hearer. Present in all language uses, the ideational function is ameaning potential, because  whatever specific use one is making of language he has to refer to categories of his experience of the world.
The Interpersonal Function embodies all uses of language to express social and personal relations. This includes the various ways the speaker enters a speech situation and performs a speech act. Because the clause is not confined to the expression of transitivity, there are non-ideational elements in the adult language system. These elements are grouped together as this metafunction in the grammar, covering a whole range of particular uses of language.
The Textual Function refers to the fact that language has mechanisms to make any stretch of spoken or written discourse into a coherent and unified text and make a living passage different from a random list of sentences. Although two sentences may have exactly the same ideational and interpersonal functions, they may be different in terms of textual coherence.