A DataLink value is an encapsulated value that contains a logical reference from the database to a file stored outside the database.
The attributes of this encapsulated value are as follows:
The characters used in a DataLink value are limited to the set defined for a URL. These characters include the uppercase (A through Z) and lower case (a through z) letters, the digits (0 through 9) and a subset of special characters ($, -, _, @, ., &, +, !, *, ", ', (, ), =, ;, /, #, ?, :, space, and comma).
The first four attributes are collectively known as the linkage attributes. It is possible for a DataLink value to have only a comment attribute and no linkage attributes. Such a value may even be stored in a column but, of course, no file will be linked to such a column.
It is important to distinguish between these DataLink references to files and the LOB file reference variables described in References to LOB or XML file reference variables. The similarity is that they both contain a representation of a file. However:
Built-in scalar functions are provided to build a DataLink value (DLVALUE) and to extract the encapsulated values from a DataLink value (DLCOMMENT, DLLINKTYPE, DLURLCOMPLETE, DLURLPATH, DLURLPATHONLY, DLURLSCHEME, DLURLSERVER).