VEGA:

A visualization grammar, a language for:
* — creating, saving and sharing interactive visualization designs
* — describe visual appearance and interactive behaviour of visualization in json
* — reactive signals that dynamically modify a visualization in response to input
event streams

Key Semantics:

The key semantics are:
* — width, height, padding, autosize (all are for specifying the size of the
visualization)
* — data (an array of data definitions, can define type, name, stream, url, and values of the
data type)

• — scales (Configurations for as to map columns of data to pixel positions or
  colors, or type of representation(for ex: categorical==> bands etc)).

• — axes (Configuration of axes)

• — marks (Graphical primitives, which are used to encode data. Has properties
  position, size, shape, color. Examples are: dot, circle, rectangle(bar-chart),
  star etc..)

• — Have sub properties encode which marks the graphical primitives
• — Encode’s Sub property enter and exit configure interactive parts when
  the mark is added or removed.
• — marks sub property hover, update configure overall interactive parts
• — each of the hover, update properties can be triggered/linked to signals
  and changed accordingly

• — A special type of mark called group is present and can contain other
  marks(for composition of graphical primitives to create complex ones)

• — signals (act as dynamic variables, or as event-listeners to use js parlance)

• — Has sub property event streams
• — Can set dynamically evaluated variables as values on events as
  defined.
• — Events can be mouse over, mouse out, click,drag etc..
• — Event streams
• — Has sub properties source, type, marktype, between, consume, filetr etc.
• — Each sub property decides which mark to change/update, based on which
  event type/user-action/data-change

• — Event streams also have CSS-style selectors

• — Legends

• — Can create legends for the visualizatinos

• — customize them with sub properties type, orient, fill, opacity, shape

• — Transforms

• — As the name implies it can transform data streams
• — Has sub properties ilke filter, stack, aggregate, bin, collect, fold,
  impute etc