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 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).
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