The applicative data model is a conceptual-level model designed to support the data modeling of expert systems. It was developed using the same modeling methodology we advocate for other applications, by designing a metaschema using its data definition language, and so it is self-descriptive. Its metaschema incorporates both types and instances of data (including itself), removing the arbitrary distinction between schema and data. The model includes a functional, extendible data manipulation language and constraint definition language. The emphasis of this model is on providing a small set of orthogonal constructs that can be combined in regular ways to model data.