== SQM

The Semantic Query Model (SQM) is Hibernate's representation of an HQL or Criteria query's semantic (meaning).  This
representation is modeled as an "abstract syntax tree" (AST) - meaning it is a structured tree of nodes where each node
represrents an atomic piece of the query.  E.g. `SqmSelectClause` represents the query's select clause as you might
imagine.  That `SqmSelectClause` is ultimately a collection of one or more `SqmSelection` references representing the
individual selections to be returned from the query (called the domain results).

=== The Model

This SQM model uses the Hibernate domain model, which is Hibernate's extension to the JPA model.  This model contains no
relational mapping information, it simply describes the domain model in mostly Java terms although it does incorporate
"classifications" of the type system.  E.g. it understand that `Customer` is an entity, but contains no information
about the tables it maps to nor its columns.

See the `design/type-system-domain.adoc` design doc.  For details about this domain model


=== Building an SQM


=== Interpreting an SQM

Ultimately Hibernate needs to talk with the database to fulfill these query executions.  This is currently a 2-step process.

First we convert the SQM into a new AST called the SQL AST.  This is an AST that is more "SQL-y".  It's nodes are defined
in terms of Hibernate's mapping model which is the model that actually does understand the relational mapping.
See `design/type-system-mapping.adoc` for details about this model.  Part of this conversion step is to resolving
domain model references to mapping model references...