Hypertext is the presentation of information as a linked network of nodes which readers are free to navigate in a non-linear fashion. It allows for multiple authors, a blurring of the author and reader functions, extended works with diffuse boundaries, and multiple reading paths.
The term "hypertext" was coined by Ted Nelson, who defined it in his self-published Literary Machines as "non-sequential writing" (0/2).
2) link :
A link is the traversable connection between two nodes . An anchor is the visible region which must be selected to activate the link. These may vary in size from one word to the entire contents of the node. For example, in this current node, the word "nodes" in the first sentence is an anchor. It is the visible part of a link between the nodes "Links and Anchors" and "Node." In theory, anchors may overlap; in practice, most systems insist on their being distinct, in order to make the underlying mechanics simpler.
3) lexia :
The lexia is a block of hypertext which is connected to other lexiae through links, which comment upon each other (some might say, dialogue with each other). Roland Barthes’ definition ( S/Z ) provides us with an understanding that this is the basic building block of the hypertextual universe: It is the atom, the letter, the point of hypertext. It is viewed nonsequentially from the perspective of the author, sequentially from the perspective of the reader, and is the embodiment of the poststructuralist ideal: brief interconnected segments whose context is provided by the lexiae that surround it in three dimensions.
4) node :
A node is an integrated and self-sufficient unit of information, small relative to the complete document. In electronic instances, nodes are often thought of as being small enough to fit on one computer screen. Janet Fiderio states that they "consist of a single concept or idea" (238). Other, grander schemes (such as Xanadu) make allowances for nodes the size of books.
Interactivity is "a process whereby students are systematically encouraged to be active participants in their own learning. It is achieved by teaching approaches that engage students in the construction of knowledge."
http://www.iath.virginia.edu/elab/hfl0037.html
http://floti.bell.ac.uk/hotpot/interactivity_definition.htm l
http://www.magnesium.net/~gregsamsa/lexiacon/archives/000001.html