{"id":4487,"date":"2022-03-09T11:08:41","date_gmt":"2022-03-09T10:08:41","guid":{"rendered":"https:\/\/www.dlvsystem.it\/dlvsite\/?page_id=4487"},"modified":"2022-03-09T11:11:41","modified_gmt":"2022-03-09T10:11:41","slug":"dlvdb-user-manual","status":"publish","type":"page","link":"https:\/\/www.dlvsystem.it\/dlvsite\/dlvdb-user-manual\/","title":{"rendered":"DLVDB User Manual"},"content":{"rendered":"
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DLVDB<\/sup> User Manual<\/h2><\/span>
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DLVSystem’s Development Team<\/h4>\n<\/div>

<\/i><\/i><\/span>Main Memory Execution<\/span><\/a><\/h4><\/div>
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In the following we describe the #import<\/code> and #export<\/code> built-ins of the DLVDB<\/sup> system. We will then also give a short introduction of the ODBC library and show how to configure a database system (PostgreSQL) to interface with DLV.<\/p>\n

Syntax<\/h3>\n

We extend DLV with an ODBC interface by adding two new built-in commands to import and export relations (predicates) from\/to a DBMS. These commands take a number of arguments providing the information needed for DBMS authentication, the relational predicate to import\/export from\/to the DBMS, and the name of the table in the DBMS.<\/p>\n

The #import command<\/h3>\n

The #import<\/code> command reads tuples from a specified table of a relational database and stores them as facts (EDB program) with a predicate name p provided by the user. The name of the imported atoms is set to p, and defines a part of the EDB program. Further EDB predicates can be added by providing input via text files. Since DLV supports only supports unsigned integer and constant data types the #import command takes a parameter which specifies a type conversion for every column of the table.<\/p>\n

The #import<\/code> command is of the form:<\/p>\n

#import(databasename,\"username\",\"password\",\"query\", predname, typeConv).<\/code><\/p>\n

where:<\/p>\n

    \n
  1. databasename<\/em> is the name of the database server;<\/li>\n
  2. username<\/em> defines the name of the user who connects to the database (the string must be enclosed by \u201d \u201c);<\/li>\n
  3. password<\/em> defines the password of that user (the string must be enclosed by \u201d \u201c);<\/li>\n
  4. query<\/em> as an SQL statement that constructs the table that will be imported (and must be quoted by \u201d \u201c);<\/li>\n
  5. predname<\/em> defines the name of the predicate that will be used;<\/li>\n
  6. typeConv<\/em> specifies the conversion for mapping DBMS data types to DLV data type; it provides a conversion for each column imported by the database.<\/li>\n<\/ol>\n

    The typeConv<\/em> parameter is a string with the following syntax: type: Conv [, Conv]<\/code>, where type: is a string constant and Conv is one of several conversion types:<\/p>\n