{\MathQL}.4 consists of a core language and of a basic library. Other
user-defined libraries can be added at will. The core language includes the
\TT{property} operator mentioned in \subsecref{HighAccess} that queries the
-underlying {\RDF} database and the infrastructure to post-process the
+underlying {\RDF} database, and the infrastructure to post-process the
query results. The components of this infrastructure are listed below:
\begin{itemize}
\item
-Explicit sets of attributed values.
-
+\textbf{Explicit sets of attributed values.}
An explicit {\av} set can be placed in a query in two forms:
-as a single quoted string, like \verb+"this is a query result"+, that
-evaluates in a single {\av} with that value and no attributes, or as a full
-{\av} set in the syntax shown in the previous sections but sorrounded by
-square brackets, like \verb+["head" attr {"attribute-name" = "contents"}]+.
-\newline
-In the second form, the contents of an attribute can be the result of a query,
-like
-\verb+["head" attr {"attribute-name" = property /"metadata" of "resource"}]+.
+as a quoted string, like \verb+"this is a query result"+, that evaluates in a
+single {\av} with that value and no attributes, or as a full {\av} set in the
+syntax shown in the previous sections but surrounded by square brackets, like
+\verb+["head" attr {/"attribute" = "contents"}]+.
\newline
-In this case the contents of the attribute are the head strings of the query
-result, whose attributes (if any) are discarded.
+In the second form, the contents of an attribute can be the result of a query
+and in this case the contents of the attribute are the head strings of the
+query result, whose attributes (if any) are discarded.
+\end{itemize}
-\item
-Variable assignment.
+\begin{center}
+\verb+["head" attr {/"attribute" = property /"metadata" of "resource"}]+
+\end{center}
+
+\begin{itemize}
+\item
+\textbf{Variable assignment.}
Variables for {\av} sets (preceded by a \TT{\$} sign and called
\emph{set variables}) can be assigned using a standard \emph{let-in}
construction and may appear wherever an {\av} set ({\ie} a query result) is
allowed.
-\newline
The assignment has the form:
\TT{let \$}\EM{variable} \TT{=} \EM{av-set} \TT{in} \EM{av-set}
so we can write:
\newline
-\verb+let $var = "contents" in ["head" attr {"attribute-name" = $var}]+.
+\verb+let $var = "contents" in ["head" attr {/"attribute" = $var}]+.
-The scope rules of {\MathQL} variables are tipical for an imperative
-programming language and any case of assignment propagation will be indicated.
+The scope of {\MathQL} variables is typical for an imperative programming
+language and any case of assignment propagation will be indicated.
\item
-Sequential composition.
-
+\textbf{Sequential composition.}
This construction has the form: \EM{av-set} \TT{;;} \EM{av-set} and works as
follows: the two {\av} sets are evaluated one after the other and the first
one is discarded but the variables assigned in the first {\av} set are
available to the second one.
\item
-Unbounded iteration.
-\newline
+\textbf{Unbounded iteration.}
This construction comes in two forms:
-\TT{while} \EM{av-set} \TT{sup} \EM{av-set}:
-\newline
-iterates the evaluation of the second {\av} set until the first {\av set} is
-empty and returns the {\MathQL} set-theoretic union of all the evaluiations
-of the second {\av set}.
-
-\TT{while} \EM{av-set} \TT{inf} \EM{av-set}:
-\newline
-like the former but set-theoretic intersection is used instead of
+\TT{while} \EM{av-set-1} \TT{sup} \EM{av-set-2}:
+iterates the evaluation of \EM{av-set-2} until \EM{av-set-1} is empty and
+returns the {\MathQL} set-theoretic union of all the evaluations of
+\EM{av-set-2}.
+\TT{while} \EM{av-set-1} \TT{inf} \EM{av-set-2}:
+like the former but the set-theoretic intersection is used instead of the
set-theoretic union.
-In order for \TT{while} to work as expected, both {\av} sets are evaluaed in
+In order for \TT{while} to work as expected, both {\av} sets are evaluated in
a common context during the iteration ({\ie} the variables defined in both
-are alailable to both) and this context is also propagated outside the
-\TT{while} for convenience.
+are available to both) and this context is also propagated outside the
+\TT{while}.
\item
-Bounded iteration.
-\newline
+\textbf{Bounded iteration.}
Also this construction comes in two forms:
\TT{for @}\EM{variable} \TT{in} \EM{av-set} \TT{sup} \EM{av-set}:
-\newline
iterates the evaluation of the second \EM{av-set} assigning the \EM{variable}
to each element in the first \EM{av-set} and builds the {\MathQL}
set-theoretic union of the obtained results.
\TT{for @}\EM{variable} \TT{in} \EM{av-set} \TT{inf} \EM{av-set}:
-\newline
-like the former but set-theoretic intersection is used instead of
+like the former but the set-theoretic intersection is used instead of the
set-theoretic union.
The variables for attributed values (preceded by a \TT{@} sign and called
\emph{element variables}) may appear wherever an {\av} set is allowed and
and in some additional places.
-\newline
The element variables are kept distinct from the set variables (therefore
\TT{\$variable} and \TT{@variable} may appear in the same query without
-abiguity).
-
+ambiguity).
Concerning the scope rules used in these constructions, the variables
assigned by the first {\av} set are available to the second {\av} set during
the iteration and the variables assigned by both {\av} sets are available
outside the \TT{for} as in the previous case.
\item
-Addition of groups.
-
+\textbf{Addition of groups.}
\TT{add} \EM{optional-flag} \EM{attribute-groups} \TT{in} \EM{av-set}
-\newline
builds an {\av} set adding the specified \EM{attribute-groups} to each element
of the given {\av} set.
If no \EM{flag} is specified the addition is set-theoretic, whereas with the
\figref{Add} shows how to build a one-element {\av} set using \TT{add}.
-\begin{figure}[ht]
+\begin{figure}
\begin{footnotesize} \begin{verbatim}
The set of attributed values given explicitly:
-["head" attr {"attribute-name" = property /"metadata" of "resource"}]
+ ["head" attr {/"attribute" = property /"metadata" of "resource"}]
-The same set built with the add operator
-add {"attribute-name" = property /"metadata" of "resource"} in "head"
+The same set built with the add operator:
+ add {/"attribute" = property /"metadata" of "resource"} in "head"
\end{verbatim} \end{footnotesize}
-\vskip-1pc
+\vspace{-1pc}
\caption{A simple use of the add operator}
\label{Add}
\end{figure}
\item
-Existential test.
-
+\textbf{Existential test.}
The existential test has the form \TT{ex} \EM{av-set} where the
specification of the {\av} set contains some instances of the construction
\TT{@}\EM{variable}\TT{.}\EM{attribute-name}, and runs as follows:
\TT{@}\EM{variable}\TT{.}\EM{attribute-name}
with the contents of \EM{attribute-name} in an attribute group of the {\av}
stored in \TT{@}\EM{variable} and the evaluation is repeated for every
-possible choice of the groups (recall that different groups are allowed to
+possible choice of these groups (recall that different groups are allowed to
contain attributes with the same name). If one evaluation gives a non empty
-result, the defaut representation of \emph{true} is returned (the test
-succeded) in the other case the empty {\av} set, {\ie} \emph{false}, is
-returned (the test failed).
+result, the default representation of \emph{true} is returned, in the other
+case the empty {\av} set, {\ie} \emph{false}, is returned.
\item
-Function invocation:
-
+\textbf{Function invocation.}
The core language allows to invoke two kinds of external functions (with
which a language extension may be provided): the functions of the first kind
return an {\av} set, the functions of the second kind return a piece of
\EM{function-name} \verb+{+
\EM{name} \TT{,} $\cdots$ \TT{,} \EM{name} \verb+} {+
\EM{av-set} \TT{,} $\cdots$ \TT{,} \EM{av-set} \verb+}+
-\newline
-invokes the specified function of the firs kind on the given arguments and
-returns it result. The \EM{name} argument are {\MathQL} paths and usually
+invokes a function of the first kind on the given arguments and returns its
+result. The \EM{name} arguments are {\MathQL} paths and usually
represent attribute names.
\TT{gen} \EM{function-name} \verb+{+
\EM{av-set} \TT{,} $\cdots$ \TT{,} \EM{av-set} \verb+}+
-\newline
-invokes the specified function of the second kind on the given arguments and
-replaces the function invocation with its result.
+invokes a function of the second kind on the given arguments and replaces
+itself with the function result.
-The function names are {\MathQL} paths exactly as the attribute nanes and the
+The function names are {\MathQL} paths exactly as the attribute names and the
graph paths used by the \TT{property} operator. The names of the two kinds of
functions are kept in distinct environments so they do not clash.
{\MathQL}.4 comes with a basic library of functions of the first kind
-(see \subsecref{IBasic}) that integrate the core language providing several
-facilities to the user.
+(see \subsecref{Basic}) that integrate the core language providing several
+facilities.
\end{itemize}
projects / helm.git / blobdiff