A DATALINK value is an encapsulated value that contains a logical reference from the database to a file stored outside the database.
The data-location attribute of this encapsulated value is a logical reference to a file in the form of a Uniform Resource Locator (URL). The value of this attribute conforms to the syntax for URLs as specified by the following BNF 119 , based on RFC 1738 : Uniform Resource Locators (URL), T. Berners-Lee, L. Masinter, M. McCahill, December 1994
The following conventions are used in the BNF specification:
The BNF specification for DATALINKs:
URL
url = httpurl | fileurl | uncurl | dfsurl | emptyurl
HTTP
httpurl = "http://" hostport [ "/" hpath ] hpath = hsegment *[ "/" hsegment ] hsegment = *[ uchar | ";" | ":" | "@" | "&" | "=" ]
Note that the search element from the original BNF in RFC1738 has been removed, because it is not an essential part of the file reference and does not make sense in DATALINKs context.
FILE
fileurl = "file://" host "/" fpath fpath = fsegment *[ "/" fsegment ] fsegment = *[ uchar | "?" | ":" | "@" | "&" | "=" ]
Note that host is not optional and the "localhost" string does not have any special meaning, in contrast with RFC1738. This avoids confusing interpretations of "localhost" in client/server and EEE configurations.
UNC
uncurl = "unc:\\" hostname "\" sharename "\" uncpath sharename = *uchar uncpath = fsegment *[ "\" fsegment ]
Supports the commonly used UNC naming convention on NT. This is not a standard scheme in RFC1738.
DFS
dfsurl = "dfs://.../" cellname "/" fpath cellname = hostname
Supports the DFS naming scheme. This is not a standard scheme in RFC1738.
EMPTYURL
emptyurl = "" hostport = host [ ":" port ] host = hostname | hostnumber hostname = *[ domainlabel "." ] toplabel domainlabel = alphadigit | alphadigit *[ alphadigit | "-" ] alphadigit toplabel = alpha | alpha *[ alphadigit | "-" ] alphadigit alphadigit = alpha | digit hostnumber = digits "." digits "." digits "." digits port = digits
Empty (zero-length) URLs are also supported for DATALINK values. These are useful to update DATALINK columns when reconcile exceptions are reported and non-nullable DATALINK columns are involved. A zero-length URL is used to update the column and cause unlink
Miscellaneous Definitions
lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
"i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
"q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
"y" | "z"
hialpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
"I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
"Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
"Y" | "Z"
alpha = lowalpha | hialpha
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
"8" | "9"
safe = "$" | "-" | "_" | "." | "+"
extra = "!" | "*" | "'" | "(" | ")" | ","
hex = digit | "A" | "B" | "C" | "D" | "E" | "F" |
"a" | "b" | "c" | "d" | "e" | "f"
escape = "%" hex hex
unreserved = alpha | digit | safe | extra
uchar = unreserved | escape
digits = 1*digit
Leading and trailing blank characters are trimmed by DB2 while parsing. Also, the scheme names ('HTTP', 'FILE', 'UNC', 'DFS') and host are case-insensitive, and are always stored in the database in uppercase.