Identifying the data type

You need to explain your question a bit more!

The operating system, can and will determine the program to use to execute or handle a file based on its extension - providing the associations have been setup correctly.

Each software program comes with its own recognized set of Data Types and an "engine" (or block of code) that processes stored values on a PC (or server). With database software (like Access or Oracle) developers MUST assign a Data Type every time they create a "bucket" to store stuff in (even if its a Data Type that accepts anything because they don't know what's coming such as a Variant Data Type). The software "engine" then tells the CPU (or PC engine) how to interpret the next incoming value as things are processed at lightning speed. The same process is esentially true for almost every type of software but only Database software (and a few spreadsheet fields) allows developers to "pre-define" Data Types.

Don't confuse Data Type with Format where format allows you to display a single Data Type (value) many different ways.

Hope this helps.