data model is a description of, in general, how the data is structured. The most common one is the rational data model. An XML document captures data, instead of a set of records, as a hierarchical structure, of labeled values. In graph data model all data is in the form of nodes and edges.
Thus a data model defines the general form of the data.
schema sets up the structure of the database, where the
data is the actual information stored within the schema. Schemas and data are like types and variables in programming. In a program there are types to set up and variables that of those types. In a database there is a schema to set up and a whole bunch of data that adheres to that schema. Typically, the schema is set up at the beginning and does not change very much where the data changes rapidly.
To set up the schema in a database, one normally uses a
data definition language. Sometimes higher level design tools are used to help to think about the Design and then from there go to the data definition language. It is used to in general to set up a scheme or structure for a particular database.
Once the data has been loaded, then it is possible to start querying and modifying the data which is typically done with a
data manipulation language in order to query and modify the database.