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Classification filters

Classification filters are used inside relational classifications to remove rows that should not be considered during evaluation.

In simple terms:

A classification filter asks: Should this row continue in the evaluation, or should it be removed?

Why classification filters exist

When relational classifications follow relations between tables, they often collect many rows.

Sometimes only a subset of those rows should be counted.

Classification filters allow the system to keep only rows that satisfy a specific condition.

Example:

A booking might only count rooms that are active.

Relation path:

Booking → Room

Filter:

Room classification: Active room

Only rooms where Active room = true will remain in the evaluation.

How classification filters work

A classification filter is applied at a specific step in a relation path.

At that step the system:

  1. Follows the relation and collects rows
  2. Evaluates the referenced classification for each row
  3. Keeps or removes rows depending on the filter rule
  4. Passes the remaining rows to the next step

Example:

Room Active room
Room 101 true
Room 102 false

If the filter is Include Active room, the result becomes:

Room
Room 101

Include vs exclude

Classification filters support two modes.

Include

Only rows where the classification is true remain.

Example:

Include classification: Active room

Result:

Only active rooms remain.

Exclude

Rows where the classification is true are removed.

Example:

Exclude classification: Maintenance room

Result:

Rooms marked as maintenance are removed from the set.

Multiple filters

Several classification filters can be applied at the same step.

In that case all filters must pass for a row to remain.

Example:

Include Active room
AND
Exclude Maintenance room

A room must satisfy both rules to stay in the result set.

Example

Tables

  • Booking
  • Room

Relation

Booking → Room

Classification filter

Include Active room

Evaluation:

Booking Rooms found Active rooms counted
B001 Room101, Room102 Room101
B002 Room103 Room103

Only the rows that pass the filter are counted in the final classification result.

A simple way to think about classification filters

A classification filter answers the question:

Which of the related rows should actually be considered?

By reusing existing classifications, filters make relational logic easier to reuse and easier to maintain.

Reference

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