Abstract
The formats CSV [RFC4180] (comma separated values)
and TSV [IANA-TSV] (tab separated values)
provide simple, easy to process formats for the transmission of tabular data.
They are supported as input datat formats to many tools, particularly spreadsheets.
This document describes their use for expressing SPARQL query results from
SELECT queries.
1. Introduction
This document describes CSV and TSV formats for expressing
the results of a SPARQL SELECT query.
They provide lowest common denominator
formats between systems using different
implementation technologies.
Other formats for expression SPARQL results are the
SPARQL XML Results Format [RDF-SPARQL-XMLRES]
and SPARQL JSON Results Format
[SPARQL11-JSON-RES].
Each format is useful in different application scenarios.
The SPARQL Results CSV Results Format is a lossy encoding
of a table of results. It does not encode all the details of
each RDF term in the results but instead just gives a string
without indicating the type of the term (IRI, Literal, Literal
with datatype, Literal with language, or blank node). This makes
it simple to consume data, such as text and numbers, in
applications without needing to understand the details
of RDF. In some applications, guesses as to which
elements are hyperlinks are made pragmatically, for example,
guessing that strings starting "http://" are links.
The SPARQL Results TSV Results Format does encode the details
of RDF terms in the results table by using the syntax that SPARQL
[SPARQL11-QUERY]
and Turtle [TURTLE] use. An application receiving a TSV-encoded
results set can
split each line into elements of the result row, and extract
all the details it wishes to process of the RDF terms by
simple string processing, without a complete XML or JSON parser
required by the more complex SPARQL result formats.
When this document uses the words must, must not, should, should
not, may and recommended, they must be interpreted as described in
RFC 2119 [RFC2119].
1.1 Example
The following artificial example is used to illustrate the
features of serializing results in each format.
| x |
literal |
| <http://example/x> |
String |
| <http://example/x> |
String-with-dquote" |
| _:b0 |
Blank node |
|
Missing 'x' |
|
|
| <http://example/x> |
|
| _:b1 |
"String-with-lang"@en |
| _:b1 |
123 |
3. CSV - Comma Separated values
In the SPARQL Results CSV Format,
the results table is serialized as one line listing the variables
in the results, using the CSV header line,
followed by one line for each query solution
(a line may end up split by newlines in the data).
Values in the results are strings, for URIs, literals and blank nodes,
together with numbers when the literals are of numeric XSD
datatype.
3.1 Serializing the Results Table
The first line of a SPARQL CSV Results Format response
is the header line giving the names of the variables
used in the result set. The header line consists of the
variable names, without leading ?, separated by commas.
While the text/csv format does not require a header row,
the SPARQL CSV Results Format must use a header row.
If the content type parameter header is used,
it must be header=present.
The remaining rows are the values of the results,
with each binding determined by the position in the row,
corresponding to the entry in the header line.
If a variable is not bound, an empty field is used (e.g. ,,).
Each row must have the same number of fields,
with each field corresponding to a binding to the variable
in the header line in the same field position.
3.2 Serializing RDF Terms
The entry in each field is the string corresponding to the RDF term value.
(c.f. SPARQL STR()) without syntax to denote what kind of
term it is. The encoding quoting rules of CSV format must be
used.
Blank nodes use the _:label form from Turtle and SPARQL.
Use of the same label indicates the same blank node within the
results but has no significance outside
the results.
Fields containing any of
" (QUOTATION MARK, code point 34, 0x22 in Unicode[UNICODE]),
, (COMMA, code point 44, 0x2C),
LF (code point 10, 0x0A) or
CR (code point 13, 0x0D)
must be quoted using the quoting mechanism
of RFC4180 [RFC4180]. Fields are limited by a pair of
quotation marks "
(code point 0x22).
Within quote strings,
all characters except ",
including new line characters have their exact meaning -
newlines do not end a CSV record.
"
is written using a pair of quotation marks
"".
The standard CSV format does not distinguish between missing
values and empty strings.
The SPARQL 1.1 CSV Results Format uses the same representation
for unbound variables as for variables bound to an empty string
literal. The other SPARQL Result formats (based on JSON, TSV or XML)
can be used if this distinction is required.
3.3 Example of CSV-Serialized Results
x,literal
http://example/x,String
http://example/x,"String-with-dquote"""
_:b0,Blank node
,Missing 'x'
,
http://example/x,
_:b1,String-with-lang
_:b1,123
4. TSV - Tab Separated values
In the SPARQL Results TSV Format,
the results table is serialized as one line listing the variables
in the results, followed by one line for each query solution.
All RDF terms used in the format are encoded in the format
specified by Turtle [TURTLE] except that the
triple quoted forms for the lexical part of literals
must not be used. These forms would allow raw newlines and
tabs that form part of the TSV format. A TSV format SPARQL result
set must use the single quoted literal forms, together with
any necessary escapes such as \t,
\n and \r.
4.1 Serializing the Results Table
The results table is serialized as one line listing the variables
in the results, followed by one line for each query solution.
This first line is required by the TSV format [IANA-TSV],
unlike CSV, where it is optional.
Variables are serialized in SPARQL syntax, using question mark
? character followed by the variable name.
Each row of the result set is serialized by sequence of
RDF terms in SPARQL syntax, separated by a tab
(Horizontal Tab, Unicode codepoint 9) character.
If a variable is not bound in a row, an empty field is used.
Each row must have the same number of fields, corresponding to the variables
listed in the first row.
4.2 Serializing RDF Terms
The SPARQL Results TSV Results Format serializes
RDF terms in the results table by using the syntax that SPARQL
[SPARQL11-QUERY]
and Turtle [TURTLE] use.
IRIs enclosed in <...>,
literals are enclosed with double quotes "..."
or single quotes ' ...'
with optional @lang or ^^ for datatype.
The quotes around the lexical
form is required.
Tab, newline and carriage return characters (Unicode codepoints
0x09, 0x0A (line feed) and 0x0D (Carriage Return))
are encoded in strings as
\t, \n and \r respectively.
The long string forms using triple quotes """ and
''' must not be used.
The abbreviated forms for numbers (XSD integers, decimals and doubles)
should be used.
Blank nodes use the _:label form from Turtle and SPARQL.
Use of the same label indicates the same blank node within the
results but has no significance outside
the results.
4.3 Example of TSV-Serialized Results
Writing <TAB> for a raw tab character (Unicode
code point 9):
?x<TAB>?literal
<http://example/x><TAB>"String"
<http://example/x><TAB>"String-with-dquote\""
_:blank0<TAB>"Blank node"
<TAB>"Missing 'x'"
<TAB>
<http://example/x><TAB>
_:blank1<TAB>"String-with-lang"@en
_:blank1<TAB>123