Halliday & Matthiessen (1999: 378):
The text base is oriented towards the ideation base and the interaction base. It provides the resources for constructing meanings from these two bases as information of a kind that can be shared as text. An ideational figure and an interpersonal move are constructed as information in the form of a message. Such a message is related to the preceding discourse and differentiates informational statuses in terms of thematicity and newsworthiness.