yap-6.3/packages/myddas/myddas.md

 The MYDDAS Data-base interface   {#myddas}
 ==============================

  The MYDDAS database project was developed within a FCT project aiming at
  the development of a highly efficient deductive database system, based
  on the coupling of the MySQL relational database system with the YAP
  Prolog system. MYDDAS was later expanded to support the ODBC interface.


   @defgroup Requirements_and_Installation_Guide Requirements and Installation Guide
  ee
  Next, we describe how to usen of the YAP with the MYDDAS System.  The
  use of this system is entirely depend of the MySQL development libraries
  or the ODBC development libraries. At least one of the this development
  libraries must be installed on the computer system, otherwise MYDDAS
  will not compile. The MySQL development libraries from MySQL 3.23 an
  above are know to work. We recommend the usage of MySQL versus ODBC,
  but it is possible to have both options installed

  At the same time, without any problem. The MYDDAS system automatically
  controls the two options. Currently, MYDDAS is know to compile without
  problems in Linux. The usage of this system on Windows has not been
  tested yet.  MYDDAS must be enabled at configure time. This can be done
  with the following options:

  + --enable-myddas

  This option will detect which development libraries are installed on the computer system, MySQL, ODBC or both, and will compile the Yap system with the support for which libraries it detects;

  + --enable-myddas-stats

  This option is only available in MySQL. It includes code to get
  statistics from the MYDDAS system;


  + --enable-top-level

  This option is only available in MySQL.  It enables the option to interact with the MySQL server in
  two different ways. As if we were on the MySQL Client Shell, and as if
  we were using Datalog.

 @defgroup MYDDAS_Architecture MYDDAS Architecture

  The system includes four main blocks that are put together through the
  MYDDAS interface: the Yap Prolog compiler, the MySQL database system, an
  ODBC level and a Prolog to SQL compiler. Current effort is put on the
  MySQL interface rather than on the ODBC interface. If you want to use
  the full power of the MYDDAS interface we recommend you to use a MySQL
  database. Other databases, such as Oracle, PostGres or Microsoft SQL
  Server, can be interfaced through the ODBC layer, but with limited
  performance and features support.

  The main structure of the MYDDAS interface is simple. Prolog queries
  involving database goals are translated to SQL using the Prolog to SQL
  compiler; then the SQL expression is sent to the database system, which
  returns the set of tuples satisfying the query; and finally those tuples
  are made available to the Prolog engine as terms. For recursive queries
  involving database goals, the YapTab tabling engine provides the
  necessary support for an efficient evaluation of such queries.

  An important aspect of the MYDDAS interface is that for the programmer
  the use of predicates which are defined in database relations is
  completely transparent. An example of this transparent support is the
  Prolog cut operator, which has exactly the same behaviour from
  predicates defined in the Prolog program source code, or from predicates
  defined in database as relations.
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Name = 'John Doe',
  Number = 123456789 ?
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Backtracking can then be used to retrieve the next row
  of the relation phonebook.  Records with particular field values may be
  selected in the same way as in Prolog. (In particular, no mode
  specification for database predicates is required). For instance:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- phonebook(Letter,'John Doe',Letter).
  Letter = 'D',
  Number = 123456789 ?
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  generates the query

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  SELECT A.Letter , 'John Doe' , A.Number
  FROM 'phonebook' A
  WHERE A.Name = 'John Doe';
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


 @defgroup View_Level_Interface View Level Interface

  @pred db view(+,+,+).



  @pred db view(+,+).


  If we import a database relation, such as an edge relation representing the edges of a directed graph, through

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_import('Edge',edge).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  sqliand we then write a query to retrieve all the direct cycles in the
  graph, such as

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- edge(A,B), edge(B,A).
  A = 10,
  B = 20 ?
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  this is clearly inefficient [3], because of relation-level
  access. Relation-level access means that a separate SQL query will be
  generated for every goal in the body of the clause. For the second
  `edge/2` goal, a SQL query is generated using the variable bindings that
  result from the first `edge/2` goal execution. If the second
  `edge/2` goal
  fails, or if alternative solutions are demanded, backtracking access the
  next tuple for the first `edge/2` goal and another SQL query will be
  generated for the second `edge/2` goal. The generation of this large
  number of queries and the communication overhead with the database
  system for each of them, makes the relation-level approach inefficient.
  To solve this problem the view level interface can be used for the
  definition of rules whose bodies includes only imported database
  predicates.  One can use the view level interface through the predicates
  db_view/3 and `db_view/2`:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_view(Conn,PredName(Arg_1,...,Arg_n),DbGoal).
  ?- db_view(PredName(Arg_1,...,Arg_n),DbGoal).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  All arguments are standard Prolog terms.  _Arg1_ through  _Argn_
  define the attributes to be retrieved from the database, while
  _DbGoal_ defines the selection restrictions and join
  conditions.  _Conn_ is the connection identifier, which again can be
  dropped. Calling predicate `PredName/n` will retrieve database
  tuples using a single SQL query generated for the  _DbGoal_.  We next show
  an example of a view definition for the direct cycles discussed
  above. Assuming the declaration:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_import('Edge',edge).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  we
  write:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_view(direct_cycle(A,B),(edge(A,B), edge(B,A))).
  yes
  ?- direct_cycle(A,B)).
  A = 10,
  B = 20 ?
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  This call generates the SQL
  statement:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  SELECT A.attr1 , A.attr2
  FROM Edge A , Edge B
  WHERE B.attr1 = A.attr2 AND B.attr2 = A.attr1;
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Backtracking, as in relational level interface, can be used to retrieve the next row of the view.
  The view interface also supports aggregate function predicates such as
  `sum`, `avg`, `count`, `min` and `max`. For
  instance:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_view(count(X),(X is count(B, B^edge(10,B)))).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  generates the query :

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  SELECT COUNT(A.attr2)
  FROM Edge A WHERE A.attr1 = 10;
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  To know how to use db `view/3`, please refer to Draxler's Prolog to
  SQL Compiler Manual.

 @defgroup Accessing_Tables_in_Data_Sources_Using_SQL Accessing Tables in Data Sources Using SQL


  @pred db_sql(+,+,?).



  @pred db_sql(+,?).



  It is also possible to explicitly send a SQL query to the database server using

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_sql(Conn,SQL,List).
  ?- db_sql(SQL,List).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  where  _SQL_ is an arbitrary SQL expression, and  _List_ is a list
  holding the first tuple of result set returned by the server. The result
  set can also be navigated through backtracking.

  Example:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_sql('SELECT * FROM phonebook',LA).
  LA = ['D','John Doe',123456789] ?
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

@defgroup Insertion_of_Rows Insertion of Rows
  @ingroup MYDDAS

 @pred db_assert(+,+).
  @pred db_assert(+).




  Assuming you have imported the related base table using
  `db_import/2` or db_import/3, you can insert to that table
  by using db_assert/2 predicate any given fact.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_assert(Conn,Fact).
  ?- db_assert(Fact).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  The second argument must be declared with all of its arguments bound to
  constants. For example assuming `helloWorld` is imported through
  `db_import/2`:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_import('Hello World',helloWorld).
  yes
  ?- db_assert(helloWorld('A' ,'Ana',31)).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  This, would generate the following query

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  INSERT INTO helloWorld
  VALUES ('A','Ana',3)
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  which would insert into the helloWorld, the following row:
  `A,Ana,31`. If we want to insert `NULL`  values into the
  relation, we call db_assert/2 with a uninstantiated variable in
  the data base imported predicate. For example, the following query on
  the YAP-prolog system:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_assert(helloWorld('A',NULL,31)).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Would insert the row: `A,null value,31` into the relation
  `Hello World`, assuming that the second row allows null values.

*/

/** @pred db insert(+,+,+).
  @pred db insert(+,+).



  This predicate would create a new database predicate, which will insert
  any given tuple into the database.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_insert(Conn,RelationName,PredName).
  ?- db_insert(RelationName,PredName).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  This would create a new predicate with name  _PredName_, that will
  insert tuples into the relation  _RelationName_. is the connection
  identifier. For example, if we wanted to insert the new tuple
  `('A',null,31)` into the relation `Hello World`, we do:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_insert('Hello World',helloWorldInsert).
  yes
  ?- helloWorldInsert('A',NULL,31).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@defgroup  Types_of_Attributes Types of AttributesL


 @pred db_get_attributes_types(+,+,?).



  @pred db_get_attributes_types(+,?).




  The prototype for this predicate is the following:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_get_attributes_types(Conn,RelationName,ListOfFields).
  ?- db_get_attributes_types(RelationName,ListOfFields).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  You can use the
  predicate `db_get_attributes types/2` or db_get_attributes_types/3, to
  know what are the names and attributes types of the fields of a given
  relation. For example:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_get_attributes_types(myddas,'Hello World',LA).
  LA = ['Number',integer,'Name',string,'Letter',string] ?
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  where <tt>Hello World</tt> is the name of the relation and <tt>myddas</tt> is the
  connection identifier.

 @defgroup  Number_of_Fields Number of Fields


  @pred db_number_of_fields(+,?).
  @pred db_number_of_fields(+,+,?).



  The prototype for this
  predicate is the following:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_number_of_fields(Conn,RelationName,Arity).
  ?- db_number_of_fields(RelationName,Arity).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  You can use the predicate db_number_of_fields/2 or
  `db_number_of_fields/3` to know what is the arity of a given
  relation. Example:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_number_of_fields(myddas,'Hello World',Arity).
  Arity = 3 ?
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  where `Hello World` is the name of the
  relation and `myddas` is the connection identifier.

 @defgroup  Describing_a_Relation Describing a Relation

  @pred db_datalog_describe(+,+).
  @pred db_datalog_describe(+).



  The db `datalog_describe/2` predicate does not really returns any
  value. It simply prints to the screen the result of the MySQL describe
  command, the same way as `DESCRIBE` in the MySQL prompt would.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_datalog_describe(myddas,'Hello World').
  +----------+----------+------+-----+---------+-------+
  |   Field  |  Type    | Null | Key | Default | Extra |
  +----------+----------+------+-----+---------+-------+
  +  Number  | int(11)  | YES  |     |   NULL  |       |
  +  Name    | char(10) | YES  |     |   NULL  |       |
  +  Letter  | char(1)  | YES  |     |   NULL  |       |
  +----------+----------+------+-----+---------+-------+
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 @pred db_describe(+,+).



  @pred db_describe(+)

  The `db_describe/3` predicate does the same action as
  db_datalog_describe/2 predicate but with one major
  difference. The results are returned by backtracking. For example, the
  last query:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_describe(myddas,'Hello World',Term).
  Term = tableInfo('Number',int(11),'YES','',null(0),'') ? ;
  Term = tableInfo('Name',char(10),'YES','',null(1),'' ? ;
  Term = tableInfo('Letter',char(1),'YES','',null(2),'') ? ;
  no
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 @defgroup Enumerating_Relations Enumeration Relations Describing_a_Relation Describing a Relation


/@pred db_datalog_show_tables(+).
  @pred db_datalog_show_tables


  If we need to know what relations exists in a given MySQL Schema, we can use
  the `db_datalog_show_tables/1` predicate. As <tt>db_datalog_describe/2</tt>,
  it does not returns any value, but instead prints to the screen the result of the
  `SHOW TABLES` command, the same way as it would be in the MySQL prompt.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_datalog_show_tables(myddas).
  +-----------------+
  | Tables_in_guest |
  +-----------------+
  |   Hello World   |
  +-----------------+
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 @pred db_show_tables(+, ?).



  @pred db_show_tables(?)




  The db_show_tables/2 predicate does the same action as
  `db_show_tables/1` predicate but with one major difference. The
  results are returned by backtracking. For example, given the last query:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_show_tables(myddas,Table).
  Table = table('Hello World') ? ;
  no
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 @defgroup  The_MYDDAS_MySQL_Top_Level The MYDDAS MySQL Top Level

  @pred db_top_level(+,+,+,+,+).
  @pred db_top_level(+,+,+,+).




  Through MYDDAS is also possible to access the MySQL Database Server, in
  the same wthe mysql client. In this mode, is possible to query the
  SQL server by just using the standard SQL language. This mode is exactly the same as
  different from the standard mysql client. We can use this
  mode, by invoking the db top level/5. as one of the following:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_top_level(mysql,Connection,Host/Database,User,Password).
  ?- db_top_level(mysql,Connection,Host/Database/Port,User,Password).
  ?- db_top_level(mysql,Connection,Host/Database/UnixSocket,User,Password).
  ?- db_top_level(mysql,Connection,Host/Database/Port/UnixSocket,User,Password).
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Usage is similar as the one described for the db_open/5 predicate
  discussed above. If the login is successful, automatically the prompt of
  the mysql client will be used.  For example:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_top_level(mysql,con1,localhost/guest_db,guest,'').
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  opens a
  connection identified by the `con1` atom, to an instance of a MySQL server
  running on host `localhost`, using database guest `db` and user `guest` with
  empty password. After this is possible to use MYDDAS as the mysql
  client.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_top_level(mysql,con1,localhost/guest_db,guest,'').
  Reading table information for completion of table and column names
  You can turn off this feature to get a quicker startup with -A

  Welcome to the MySQL monitor.
  Commands end with ; or \g.

  Your MySQL connection id is 4468 to server version: 4.0.20
  Type 'help;' or '\h' for help.
  Type '\c' to clear the buffer.
  mysql> exit
  Bye
  yes
  ?-
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 @defgroup   Other_MYDDAS_Properties Other MYDDAS Properties

  @pred db_verbose(+).


  When we ask a question to YAP, using a predicate asserted by
  db_import/3, or by db_view/3, this will generate a SQL
  `QUERY`. If we want to see that query, we must to this at a given
  point in our session on YAP.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_verbose(1).
  yes
  ?-
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  If we want to
  disable this feature, we must call the `db_verbose/1` predicate with the value 0.

  @pred db_top_level(+,+,+,+).

 @pred db_module(?).





  When we create a new database predicate, by using db_import/3,
  db_view/3 or db_insert/3, that predicate will be asserted
  by default on the `user` module. If we want to change this value, we can
  use the db_module/1 predicate to do so.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_module(lists).
  yes
  ?-
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  By executing this predicate, all of the predicates asserted by the
  predicates enumerated earlier will created in the lists module.
  If we want to put back the value on default, we can manually put the
  value user. Example:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_module(user).
  yes
  ?-
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  We can also see in what module the predicates are being asserted by doing:

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_module(X).
  X=user
  yes
  ?-
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 @pred db_my_result_set(?).

  The MySQL C API permits two modes for transferring the data generated by
  a query to the client, in our case YAP. The first mode, and the default
  mode used by the MYDDAS-MySQL, is to store the result. This mode copies all the
  information generated to the client side.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_my_result_set(X).
  X=store_result
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  The other mode that we can use is use result. This one uses the result
  set created directly from the server. If we want to use this mode, he
  simply do

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?- db_my_result_set(use_result).
  yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  After this command, all
  of the database predicates will use use result by default. We can change
  this by doing again `db_my_result_set(store_result)`.

 @pred db_my_sql_mode(+Conn,?SQL_Mode).



  @pred db_my_sql_mode(?SQL_Mode).




  The MySQL server allows the user to change the SQL mode. This can be
  very useful for debugging proposes. For example, if we want MySQL server
  not to ignore the INSERT statement warnings and instead of taking
  action, report an error, we could use the following SQL mode.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ?-db_my_sql_mode(traditional). yes
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  You can see the available SQL Modes at the MySQL homepage at
  <http://www.mysql.org>.