That was larger than intended, and I have more 
In a definition of Dystopian Fiction, John Joseph Adams makes this comment:
"In a dystopian story, society itself is typically the antagonist; it is society that is actively working against the protagonist’s aims and desires. This oppression frequently is enacted by a totalitarian or authoritarian government, resulting in the loss of civil liberties and untenable living conditions, caused by any number of circumstances, such as world overpopulation, laws controlling a person’s sexual or reproductive freedom, and living under constant surveillance" (Adams, 2011).
In "Lexicon" society is the antagonist - a society where technology is used to classify people ("Are you a dog or a cat person?" etc). The work of the Poet organisation is directly in contrast to Emily's aims and desires: she wants to retain her own name (Emily) on becoming a poet - she cannot, she wants to be allowed to have a relationship with another poet -she cannot, she finds a way to make a happy life for herself in Broken hill - the Poets take that away from her. There is a loss of civil liberty - mind control, particularly in Emily's case where she is forced to commit an awful act in direct contrast to her own wishes. The circumstances causing this include living under surveillance and laws controlling sexual freedom (in fact, in Emily's case, this seems to be the main motivating factor).
The article also makes the following relevant points:
"Some common themes found in dystopian fiction include mastery of nature—to the point that it becomes barren, or turns against humankind; technological advances that enslave humans or regiment their lives; the mandatory division of people into castes or groups with specialized functions; and a collective loss of memory and history making mankind easier to manipulate psychologically and ultimately leading to dehumanization"
"Discussions regarding personal freedom, the role of free will, the value of individual resistance to dictatorships, and the power of technology to transform people’s lives are also typical characteristics of dystopian fiction."
On [http://www.readwritethink.org/files/resources/lesson_images/lesson926/DefinitionCharacteristics.pdf this] website, the
"Dystopia: A futuristic, imagined universe in which oppressive societal control and the illusion of a perfect society are maintained through corporate, bureaucratic, technological, moral, or totalitarian control. Dystopias, through an exaggerated worst-case scenario, make a criticism about a current trend, societal norm, or political system"
"Lexicon" fits the bulk of this definition: it is imagined (in the sense that aspects of the world are not real), the poet's maintain an illusion of a perfect society, where people are controlled by thoughts / through technology (but we are aware that this is an illusion as the main character deviates from this right from the outset), and the novel itself is an interesting discussion / criticism of the current trend / societal norm of seemingly random questionnaires, technology controlling what we see (currently this applies to adverts on websites we visit which are targeted towards us), but in Barry's world, this has been advanced further so that entire websites are constructed based on information we have revealed through technology.
It also lists the Characteristics of a Dystopian Society, a number of which are relevant to this novel:
• Propaganda is used to control the citizens of society (signs on the gates at Broken Hill, false reporting of the events in the area, words in all areas designed to exercise control over the general public)
• Information, independent thought, and freedom are restricted (I don't need to explain the parallel's here, do I?)
• A figurehead or concept is worshipped by the citizens of the society (Yeats is worshipped by the poets in the sense that he represents the best they can be in their line of work)
• Citizens are perceived to be under constant surveillance (they are under constant surveillance)
• Citizens have a fear of the outside world (the poet's are afraid of life outside of their faction)
• Citizens live in a dehumanized state (discussed earlier)
• The natural world is banished and distrusted (nothing can be trusted to be real with the poet's around - their is always a sense that they are controlling the outcome)
• Citizens conform to uniform expectations. Individuality and dissent are bad (particularly clear in the Poet's)
• The society is an illusion of a perfect utopian world (the world looks idyllic in a sense - people only get information they want or need, the concept of being a Poet initially looks like the perfect world - the idea of being able to control others with language appears utopian, but the novel subverts this and shows us what happens when this goes wrong.
Have you had enough yet? because I have more...