While multiple arrays of the same data type can be combined into a single array by adding another dimension, there are cases where arrays related to the main data array may have different data types, for example, arrays of flags or weights. Arrays of values with different data types can in principle be stored in the same file by making them different array fields in the same row of a binary table (section 5.2.4.2), but, in practice, many find it simpler to put the arrays containing data types different from the primary data array in separate extensions. For this purpose, the IUE project developed the image extension type (Ponz, Thompson, and Muñoz 1994).