\subsection{Textual syntax} \label{Textual}
-The syntax of grammatical productions resembles BNF and POSIX notation:
+In this section we present {\MathQL}.4 textual syntax using the same notation
+that we adopted in \cite{GS03,Gui03}. In particular the grammatical
+productions we use resemble {\BNF} with some {\POSIX} formalism:
\begin{itemize}
\TT{::=} defines a grammatical production by means of a regular expression.
Regular expressions are made of the following elements
-(here \TT{...} is a placeholder):
-
-% \item
-% \TT{.} represents any character between U 0020 and U 007F inclusive;
+(\TT{...} is a placeholder):
\item
\TT{`...`} represents any character in a character set;
\item
-\verb+`^ ...`+ represents any character (U+0020 to U+007E) not in a character
-set;
+\verb+`^ ...`+ represents any character (U+20 to U+7E) not in a character set;
\item
\TT{"..."} represents a string to be matched verbatim;
\end{itemize}
-\noindent
-{\MathQL} Expressions can contain quoted constant strings with the syntax of
-\figref {StrTS}.%
-\footnote{Note that the first slash of the \GP{path} is not optional as
-in {\MathQL}.3.}
-
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
<dec> ::= '0 - 9'
<num> ::= <dec> [ <dec> ]*
\caption{Textual syntax of numbers, strings and paths} \label{StrTS}
\end{figure}
-\noindent
-The meaning of the escaped sequences is shown in \figref{EscTS}
-(where $ .... $ is a 4-digit placeholder).
-
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize}
\begin{center} \begin{tabular}{|l|l|c|}
\hline {\bf Escape sequence} & {\bf Unicode character} & {\bf Text} \\
\caption{Textual syntax of escaped characters} \label{EscTS}
\end{figure}
+Queries and results can contain quoted constant strings with the syntax of
+\figref {StrTS}%
+\footnote
+{Note that the first slash of the \GP{path} is not optional as in {\MathQL}.3.}
+and the meaning of the escaped sequences is shown in \figref{EscTS} (where
+$ .... $ is a 4-digit placeholder).
{\MathQL} character escaping syntax aims at complying with W3C character model
for the World Wide Web \cite{W3Ca} which recommends a support for standard
Unicode characters (U+0000 to U+FFFF) and escape sequences with start/end
delimiters.
In particular {\MathQL} escape delimiters (backslash and caret) are chosen
-among the {\em unwise} characters for URI references (see \cite{URI}) because
-URI references are the natural content of constant strings and these
-characters should not be so frequent in them.
-
-Query expressions can contain variables for {\av}'s (production \GP{avar})
-and variables for {\av} sets, {\ie} for query results (production \GP{svar})
-according to the syntax of \figref{VarTS}.%
-\footnote{This syntax resembles the one of programming languages identifiers.}
+among the \emph{unwise} characters for {\URI} references (see \cite{URI})
+because {\URI} references are the natural content of constant strings and
+these characters should not be so frequent in them.
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
<alpha> ::= [ 'A - Z' | 'a - z' | `_` ]+
<id> ::= <alpha> [ <alpha> | <dec> ]*
-<avar> ::= "@" <id>
<svar> ::= "$" <id>
+<evar> ::= "@" <id>
\end{verbatim}\end{footnotesize} %$
\vskip-1pc
\caption{Textual syntax of variables} \label{VarTS}
\end{figure}
-\noindent
-The syntax of query expressions (production \GP{query}) is described in
-\figref{QueryTS}.
+Queries can also contain \emph{set} variables (production \GP{svar}) and
+\emph{element} variables (production \GP{evar}) according to the syntax of
+\figref{VarTS}.%
+\footnote{This syntax resembles the one of programming languages identifiers.}
+A set variable holds an {\av} set, {\ie} a query result, while an element
+variable holds an {\av}.
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
-<qualifier> ::= [ "inverse" ]? [ "sub" | "super" ]? <path>
+<ref> ::= [ "sub" | "super" ]?
+<qualifier> ::= [ "inverse" ]? <ref> <path>
<main> ::= [ "main" <path> ]?
<cons> ::= <path> [ "in" | "match" ] <query>
<istrue> ::= [ "istrue" <cons> [ "," <cons> ]* ]?
<sec> ::= [ "attr" <exp> [ "," <exp> ]* ]?
<opt_args> ::= <main> <istrue> <isfalses> <sec>
<source> ::= [ "pattern" ]? <query>
-<paths> ::= [ <path> [ "," <path> ]* ]?
+<paths> ::= <path> [ "," <path> ]*
<query> ::= "(" <query> ")" | <string> | "[" <xavs> "]"
| "property" <qualifier> <opt_args> "of" <source>
| "let" <svar> "=" <query> "in" <query>
- | <query> ";;" <query> | <svar> | <avar>
- | "ex" <query> | <
avar> "." <path>
- | "add" [ "distr" ]? [ <xgroups> | <avar> ] "in" <query>
- | "for" <avar> "in" <query> [ "sup" | "inf" ] <query>
+ | <query> ";;" <query> | <svar> | <evar>
+ | "ex" <query> | <
evar> "." <path>
+ | "add" [ "distr" ]? [ <xgroups> | <evar> ] "in" <query>
+ | "for" <evar> "in" <query> [ "sup" | "inf" ] <query>
| "while" <query> [ "sup" | "inf" ] <query>
- | <path> "{" <paths> "}" "{" <queries> "}"
+ | <path> "{" [ <paths> ]? "}" "{" <queries> "}"
| "gen" <path> [ "{" <queries> "}" | "in" <query> ]
<queries> ::= [ <query> [ "," <query> ]* ]?
<xattr> ::= <path> "=" <query>
\caption{Textual syntax of queries} \label{QueryTS}
\end{figure}
-\noindent
-The syntax of result expressions (production \GP{avs}) is described in
-\figref{ResultTS}.
-
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
<attr> ::= <path> "=" <string> | "{" <string> [ "," <string> ]* "}"
<group> ::= "{" <attr> [ ";" <attr> ]* "}"
\caption{Textual syntax of results} \label{ResultTS}
\end{figure}
-The textual syntax of the language extension provided by the basic library
-is in \figref{BasicTS}.
-
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
<query> ::= "empty" | "false" | "true"
- | "not" <query>
- | <query> [ "and" | "or" | "xor"| "sub" | "meet" | "eq" | "le"| "lt" ] <query>
- | <query> [ "union" | "intersect" ] <query> | { <queries> }
+ | [ "not" | "count" | "proj" <path> "of" ] <query>
+ | <query> [ "and" | "or" | "xor" ] <query>
+ | <query> [ "sub" | "meet" | "eq" | "le" | "lt" ] <query>
+ | <query> [ "union" | "intersect" | "diff" ] <query>
+ | "{" <queries> "}"
+ | "keep" [ "allbut" ]? [ <paths> "in" ]? <query>
| "if" <query> "then" <query> "else" <query>
- | "select" <avar> "from" <query> "where" <query>
+ | "select" <evar> "from" <query> "where" <query>
\end{verbatim} \end{footnotesize}
\vskip-1pc
-\caption{Textual syntax of basic extension} \label{BasicTS}
+\caption{Textual syntax of the basic extension} \label{BasicTS}
\end{figure}
+The core infrastructure of {\MathQL}.4 defines a syntax for queries
+(\figref{QueryTS}, production \GP{query}) and a syntax for results
+(\figref{ResultTS}, production \GP{avs}).
+A syntax extension for the most common functions of the basic library is
+also provided for the user's convenience and for backward compatibility with
+{\MathQL}.3. The syntax extension concerning the functions covered in this
+paper is shown in \figref{BasicTS}.
+Note that this extension makes \GP{avs} an instance of \GP{xavs}.
+
+
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