Checking the metadata involves validating the source and the target table structure w.r.t. the mapping document. The mapping document has details of the source and target columns, data transformations rules and the data types, all the fields that define the structure of tables in the source and the target systems.
The length of target column data type should be equal to or greater than the source column data type. Let us take an example. Suppose you have the first names and the last names in the source table and the data length for each is defined as 50 characters. Then, the target data length for full name column in the target system should be a minimum of 100 or more.
Data type checking involves verifying the source and the target data type and ensuring that they are same. There is a possibility that the target data type is different from the source data after a transformation. Hence there is a need to check the transformation rules as well.
Constraint checking involves verifying the index values and constraints as per the design specification document. All the columns that cannot have Null values should have Not Null constraint. Primary keys columns are indexed as per the design document.