A projection is a special case of a 
materialized view that provides physical storage for data. A projection can contain some or all of the columns of one or more tables. A projection that contains all of the columns of a table is called a superprojection. A projection that joins one or more tables is called a pre-join projection. Most projections are used for ad-hoc query processing and K-safety but it is possible to have query-specific projections.
A superprojection is a projection that contains every column of a table in the Logical Schema. A table can have multiple superprojections with different sort orders.
A materialized view is similar to a standard SQL view with one major exception: the data is actually stored on disk rather than computed each time the view is used in a query. A materialized view, then, must be refreshed whenever the data in the underlying tables is changed. A projection is a special case of a materialized view.
