Classes & Attributes

You have already seen classes in passing, one renamed and one promoted in the previous lecture. This lecture makes the definitions explicit: what classes and attributes are, how both are anchored to the database with a sql tag, and which type each attribute should get.

Key points

• Class: a core business concept people ask about, such as customer, product or region. The Knowledge Graph is built around them.
• Two kinds of classes: a parent class is usually defined from a table, so one row is one instance. An attribute class lives inside a parent class and is defined by a single column.
• Attributes: everything a class carries - attribute classes, numbers, booleans, strings and dates.
• The sql tag: tells Veezoo what to use in the generated SQL. For an attribute that is its column, and for a parent class it is a value that is unique per row, usually an ID.
• Class or not: a column deserves to be a class when it holds a smallish, finite set of values worth recognising individually, such as regions or product categories.
• Numbers and booleans: numbers are values Veezoo computes on - sums, averages, and the KPIs built on them. Booleans are binary flags such as online versus offline.
• Strings and dates: strings are free text searched with contains, and dates are points in time that come as a year, a date or a date with time.
• Relationships: connect classes to each other and get their own lecture later in this module.

Check your understanding