Simpler xotl.ql.interfaces.ITerm interface

This proposes to simplify the xotl.ql.interfaces.ITerm to remove the parent attribute. The main reason is to make the query object closer to the syntactical structure of the expression.

XEP:1 – Simpler xotl.ql.interfaces.ITerm interface Status:Obsolete, Removed Author:Manuel Vázquez Acosta Branch:none

Rationale

Currently, the interface for ITerm has a parent attribute. That attribute relates a term to another in the same way a getattr operation would do.

So it may be argued that this is actually an operation expressed by the dot operator, and not a term hierarchy. In fact, at the syntactical level there’s no such thing as a parent-child hierarchy for terms; just a <term> DOT <term> is present at that level.

This XEP proposed that the expression:

parent.child

Be represented equivalently to:

getattribute(parent, 'child')

Inclusion rationale

Changes in the API

There are two changes in the API:

• The removal of parent since it won’t be needed any more.
• The generalization of xotl.ql.interfaces.IGeneratorToken to support expressions.

Currently a translator must have a look-up table from token’s terms to current objects (names); and must take into account that every term in filters is bound to a token.

Let’s see how this might work in a relational setting for the query:

these(child
      for parent in this
      if parent.children & parent.age > 34
      for child in parent.children
      if child.age < 6)

Non-inclusion rationale

The current implementation complies better with an AST than resorting to transform the DOT into a getattribute.

If a translator is best understood (or implemented) by doing that transformation, it may do so internally.

It’s probably easier with current ITerm to see if we need to correlate two terms (i.e emitting a JOIN in a SQL query) by looking at the term’s parents. And it should not be complicated to know how to fetch an attribute from, given that binding is inherited from parents.