1. A computer-implemented method of defining and registering a user-defined data conversion algorithm in a shared data store of a distributed database system for selective use on data entered into or retrieved from the database system, comprising: defining by a user a plurality of functions that comprise and mathematically express operations of the user-defined data conversion algorithm, said defining comprising defining implementations and parameters for each of said functions, each of the functions having associated arguments corresponding to said parameters, and wherein said data conversion algorithm comprises one of data compression, data decompression, data encryption or data decryption; converting by the computer the implementations for each of the plurality of functions into separate executable code objects, each code object comprising an implementation of one of said plurality of functions and having associated parameters of an argument of said one of said plurality of functions, and storing said code objects and said associated parameters in a shared library of the data store with a common global identifier that uniquely identifies the user-defined data conversion algorithm and ties together each of said code objects as corresponding to implementations of said one of said functions of the user-defined data conversion algorithm; registering each of said code objects and said associated parameters in a catalog of the data store with said common global identifier to enable said code objects and said associated parameters corresponding to an implementation of a function of said data conversion algorithm to be separately and selectively accessed, changed and applied to the data by a user; and further comprising automatically and transparently converting data entered into or retrieved from the data store using said data conversion algorithm in response to a data conversion statement referencing the common global identifier in data store commands to enter data into and retrieve data from the data store.