1 Oracle Semantic Technologies Overview

1.3.1 Metadata for Models

The MDSYS.SEM_MODEL$ view contains information about all models defined in the database. When you create a model using the SEM_APIS.CREATE_SEM_MODEL procedure, you specify a name for the model, as well as a table and column to hold references to the semantic data, and the system automatically generates a model ID.

Oracle maintains the MDSYS.SEM_MODEL$ view automatically when you create and drop models. Users should never modify this view directly. For example, do not use SQL INSERT, UPDATE, or DELETE statements with this view.

The MDSYS.SEM_MODEL$ view contains the columns shown in Table 1-1.

When you create a model, a view for the triples associated with the model is also created under the MDSYS schema. This view has a name in the format RDFM_model-name, and it is visible only to the owner of the model and to users with suitable privileges. Each MDSYS.SEMM_model-name view contains a row for each triple (stored as a link in a network), and it has the columns shown in Table 1-2.

1.3.2 Statements

The MDSYS.RDF_VALUE$ table contains information about the subjects, properties, and objects used to represent RDF statements. It uniquely stores the text values (URIs or literals) for these three pieces of information, using a separate row for each part of each triple.

Oracle maintains the MDSYS.RDF_VALUE$ table automatically. Users should never modify this view directly. For example, do not use SQL INSERT, UPDATE, or DELETE statements with this view.

The RDF_VALUE$ table contains the columns shown in Table 1-3.

<eg:a> <eg:b> "123"^^http://www.w3.org/2001/XMLSchema#int
<eg:a> <eg:b> "123"^^http://www.w3.org/2001/XMLSchema#unsignedByte

1.3.3 Subjects and Objects

RDF subjects and objects are mapped to nodes in a semantic data network. Subject nodes are the start nodes of links, and object nodes are the end nodes of links. Non-literal nodes (that is, URIs and blank nodes) can be used as both subject and object nodes. Literals can be used only as object nodes.

1.3.4 Blank Nodes

Blank nodes can be used as subject and object nodes in the semantic network. Blank node identifiers are different from URIs in that they are scoped within a semantic model. Thus, although multiple occurrences of the same blank node identifier within a single semantic model necessarily refer to the same resource, occurrences of the same blank node identifier in two different semantic models do not refer to the same resource.

In an Oracle semantic network, this behavior is modeled by requiring that blank nodes are always reused (that is, are used to represent the same resource if the same blank node identifier is used) within a semantic model, and never reused between two different models. Thus, when inserting triples involving blank nodes into a model, you must use the SDO_RDF_TRIPLE_S constructor that supports reuse of blank nodes.

1.3.5 Properties

Properties are mapped to links that have their start node and end node as subjects and objects, respectively. Therefore, a link represents a complete triple.

When a triple is inserted into a model, the subject, property, and object text values are checked to see if they already exist in the database. If they already exist (due to previous statements in other models), no new entries are made; if they do not exist, three new rows are inserted into the RDF_VALUE$ table (described in Section 1.3.2).

1.3.6 Inferencing: Rules and Rulebases

Inferencing is the ability to make logical deductions based on rules. Inferencing enables you to construct queries that perform semantic matching based on meaningful relationships among pieces of data, as opposed to just syntactic matching based on string or other values. Inferencing involves the use of rules, either supplied by Oracle or user-defined, placed in rulebases.

Figure 1-2 shows triple sets being inferred from model data and the application of rules in one or more rulebases. In this illustration, the database can have any number of semantic models, rulebases, and inferred triple sets, and an inferred triple set can be derived using rules in one or more rulebases.

Figure 1-2 Inferencing

Description of "Figure 1-2 Inferencing"

A rule is an object that can be applied to draw inferences from semantic data. A rule is identified by a name and consists of:

• An IF side pattern for the antecedents

• An optional filter condition that further restricts the subgraphs matched by the IF side pattern

• A THEN side pattern for the consequents

For example, the rule that a chairperson of a conference is also a reviewer of the conference could be represented as follows:

('chairpersonRule', -- rule name
 '(?r :ChairPersonOf ?c)', -- IF side pattern
 NULL,  -- filter condition
 '(?r :ReviewerOf ?c)', -- THEN side pattern
 SEM_ALIASES (SEM_ALIAS('', 'http://some.org/test/'))
)

In this case, the rule does not have a filter condition, so that component of the representation is NULL. Note that a THEN side pattern with more than one triple can be used to infer multiple triples for each IF side match.

A rulebase is an object that contains rules. The following Oracle-supplied rulebases are provided:

• RDFS

• RDF (a subset of RDFS)

• OWLSIF (empty)

• RDFS++ (empty)

• OWLPRIME (empty)

The RDFS and RDF rulebases are created when you call the SEM_APIS.CREATE_SEM_NETWORK procedure to add RDF support to the database. The RDFS rulebase implements the RDFS entailment rules, as described in the World Wide Web Consortium (W3C) RDF Semantics document at http://www.w3.org/TR/rdf-mt/. The RDF rulebase represents the RDF entailment rules, which are a subset of the RDFS entailment rules. You can see the contents of these rulebases by examining the MDSYS.SEMR_RDFS and MDSYS.SEMR_RDF views.

You can also create user-defined rulebases using the SEM_APIS.CREATE_RULEBASE procedure. User-defined rulebases enable you to provide additional specialized inferencing capabilities.

For each rulebase, a system table is created to hold rules in the rulebase, along with a system view with a name in the format MDSYS.SEMR_rulebase-name (for example, MDSYS.SEMR_FAMILY_RB for a rulebase named FAMILY_RB). You must use this view to insert, delete, and modify rules in the rulebase. Each MDSYS.SEMR_rulebase-name view has the columns shown in Table 1-4.

Information about all rulebases is maintained in the MDSYS.SEM_RULEBASE_INFO view, which has the columns shown in Table 1-5 and one row for each rulebase.

Example 1-1 creates a rulebase named family_rb, and then inserts a rule named grandparent_rule into the family_rb rulebase. This rule says that if a person is the parent of a child who is the parent of a child, that person is a grandparent of (that is, has the grandParentOf relationship with respect to) his or her child's child. It also specifies a namespace to be used. (This example is an excerpt from Example 1-10 in Section 1.9.2.)

EXECUTE SEM_APIS.CREATE_RULEBASE('family_rb');

INSERT INTO mdsys.semr_family_rb VALUES(
  'grandparent_rule',
  '(?x :parentOf ?y) (?y :parentOf ?z)',
  NULL,
  '(?x :grandParentOf ?z)', 
  SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')));

You can specify one or more rulebases when calling the SEM_MATCH table function (described in Section 1.6), to control the behavior of queries against semantic data. Example 1-2 refers to the family_rb rulebase and to the grandParentOf relationship created in Example 1-1, to find all grandfathers (grandparents who are male) and their grandchildren. (This example is an excerpt from Example 1-10 in Section 1.9.2.)

-- Select all grandfathers and their grandchildren from the family model.
-- Use inferencing from both the RDFS and family_rb rulebases.
SELECT x, y
  FROM TABLE(SEM_MATCH(
    '(?x :grandParentOf ?y) (?x rdf:type :Male)',
    SEM_Models('family'),
    SEM_Rulebases('RDFS','family_rb'), 
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')),
    null));

For information about support for native OWL inferencing, see Section 2.2.

1.3.7 Rules Indexes

A rules index is an object containing precomputed triples that can be inferred from applying a specified set of rulebases to a specified set of models. If an SEM_MATCH query refers to any rulebases, a rules index must exist for each rulebase-model combination in the query.

To create a rules index, use the SEM_APIS.CREATE_RULES_INDEX procedure. To drop (delete) a rules index, use the SEM_APIS.DROP_RULES_INDEX procedure.

When you create a rules index, a view for the triples associated with the rules index is also created under the MDSYS schema. This view has a name in the format SEMI_rules-index-name, and it is visible only to the owner of the rules index and to users with suitable privileges. Each MDSYS.SEMI_rules-index-name view contains a row for each triple (stored as a link in a network), and it has the same columns as the SEMM_model-name view, which is described in Table 1-2 in Section 1.3.1.

Information about all rules indexes is maintained in the MDSYS.SEM_RULES_INDEX_INFO view, which has the columns shown in Table 1-6 and one row for each rules index.

Information about all database objects, such as models and rulebases, related to rules indexes is maintained in the MDSYS.SEM_RULES_INDEX_DATASETS view. This view has the columns shown in Table 1-7 and one row for each unique combination of values of all the columns.

Example 1-3 creates a rules index named family_rb_rix_family, using the family model and the RDFS and family_rb rulebases. (This example is an excerpt from Example 1-10 in Section 1.9.2.)

BEGIN
  SEM_APIS.CREATE_RULES_INDEX(
    'rdfs_rix_family',
    SEM_Models('family'),
    SEM_Rulebases('RDFS','family_rb'));
END;
/

1.3.8 Semantic Data Security Considerations

The following database security considerations apply to the use of semantic data:

• When a model or rules index is created, the owner gets the SELECT privilege with the GRANT option on the associated view. Users that have the SELECT privilege on these views can perform SEM_MATCH queries against the associated model or rules index.

• When a rulebase is created, the owner gets the SELECT, INSERT, UPDATE, and DELETE privileges on the rulebase, with the GRANT option. Users that have the SELECT privilege on a rulebase can create a rules index that includes the rulebase. The INSERT, UPDATE, and DELETE privileges control which users can modify the rulebase and how they can modify it.

• To perform data manipulation language (DML) operations on a model, a user must have DML privileges for the corresponding base table.

• The creator of the base table corresponding to a model can grant privileges to other users.

• To perform data manipulation language (DML) operations on a rulebase, a user must have the appropriate privileges on the corresponding database view.

• The creator of a model can grant SELECT privileges on the corresponding database view to other users.

• A user can query only those models for which that user has SELECT privileges to the corresponding database views.

• Only the creator of a model or a rulebase can drop it.

1.5.1 Constructors for Inserting Triples Without Any Blank Nodes

The following constructor formats are available for inserting triples into a model table. The only difference is that in the second format the data type for the object is CLOB, to accommodate very long literals.

SDO_RDF_TRIPLE_S (
  model_name VARCHAR2, -- Model name
  subject    VARCHAR2, -- Subject
  property   VARCHAR2, -- Property
  object     VARCHAR2) -- Object
  RETURN     SELF;

SDO_RDF_TRIPLE_S (
  model_name VARCHAR2, -- Model name
  subject    VARCHAR2, -- Subject
  property   VARCHAR2, -- Property
  object     CLOB) -- Object
  RETURN SELF;

GET_OBJ_VALUE() RETURN VARCHAR2;

Example 1-5 uses the first constructor format to insert a triple.

INSERT INTO articles_rdf_data VALUES (2,
  SDO_RDF_TRIPLE_S ('articles','<http://www.nature.com/nature/Article1>',
    '<http://purl.org/dc/elements/1.1/creator>',
    '"Jane Smith"'));

1.5.2 Constructors for Inserting Triples With or Without Any Blank Nodes

The following constructor formats are available for inserting triples referring to blank nodes into a model table. The only difference is that in the second format the data type for the fourth attribute is CLOB, to accommodate very long literals.

SDO_RDF_TRIPLE_S (
  model_name VARCHAR2, -- Model name
  sub_or_bn  VARCHAR2, -- Subject or blank node
  property   VARCHAR2, -- Property
  obj_or_bn  VARCHAR2, -- Object or blank node
  bn_m_id    NUMBER) -- ID of the model from which to reuse the blank node
  RETURN SELF;

SDO_RDF_TRIPLE_S (
  model_name VARCHAR2, -- Model name
  sub_or_bn  VARCHAR2, -- Subject or blank node
  property   VARCHAR2, -- Property
  object     CLOB, -- Object
  bn_m_id    NUMBER) -- ID of the model from which to reuse the blank node
  RETURN SELF;

If the value of bn_m_id is positive, it must be the same as the model ID of the target model.

Example 1-6 uses the first constructor format to insert a triple that reuses a blank node for the subject.

INSERT INTO nsu_data VALUES (SDO_RDF_TRIPLE_S(
  'nsu', 
  '_:BNSEQN1001A', 
  '<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>', 
  '<http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>', 
  4));

1.6.1 Performing Queries with Incomplete or Invalid Rules Indexes

You can query semantic data even when the relevant rules index does not have a valid status if you specify the string value INCOMPLETE or INVALID for the index_status attribute of the SEM_MATCH table function. (The rules index status is stored in the STATUS column of the MDSYS.SEM_RULES_INDEX_INFO view, which is described in Section 1.3.7. The SEM_MATCH table function is described in Section 1.6.)

The index_status attribute value affects the query behavior as follows:

• If the rules index has a valid status, the query behavior is not affected by the value of the index_status attribute.

• If you provide no value or specify a null value for index_status, the query returns an error if the rules index does not have a valid status.

• If you specify the string INCOMPLETE for the index_status attribute, the query is performed if the status of the rules index is incomplete or valid.

• If you specify the string INVALID for the index_status attribute, the query is performed regardless of the actual status of the rules index (invalid, incomplete, or valid).

However, the following considerations apply if the status of the rules index is incomplete or invalid:

• If the status is incomplete, the content of a rules index may be approximate, because some triples that are inferable (due to the recent insertions into the underlying models) may not actually be present in the rules index, and therefore results returned by the query may be inaccurate.

• If the status is invalid, the content of the rules index may be approximate, because some triples that are no longer inferable (due to recent modifications to the underlying models or rulebases, or both) may still be present in the rules index, and this may affect the accuracy of the result returned by the query. In addition to possible presence of triples that are no longer inferable, some inferable rows may not actually be present in the rules index.

1.7.1 Bulk Loading Semantic Data Using a Staging Table

You can load semantic data (and optionally associated non-semantic data) in bulk using a staging table. The data must first be parsed to check for syntax correctness and then loaded into the staging table. Then, you can call the SEM_APIS.BULK_LOAD_FROM_STAGING_TABLE procedure (described in Chapter 3).

The following example shows the format for the staging table, including all required columns and the required names for these columns:

CREATE TABLE stage_table (
                     RDF$STC_sub varchar2(4000) not null,
                     RDF$STC_pred varchar2(4000) not null,
                     RDF$STC_obj varchar2(4000) not null,
                     RDF$STC_sub_ext varchar2(64),
                     RDF$STC_pred_ext varchar2(64),
                     RDF$STC_obj_ext varchar2(64),
                     RDF$STC_canon_ext varchar2(64)
);

If you also want to load non-semantic data, specify additional columns for the non-semantic data in the CREATE TABLE statement. The non-semantic column names must be different form the names of the required columns. The following example creates the staging table with two additional columns (SOURCE and ID) for non-semantic attributes.

CREATE TABLE stage_table_with_extra_cols (
                     source VARCHAR2(4000),
                     id NUMBER,
                     RDF$STC_sub varchar2(4000) not null,
                     RDF$STC_pred varchar2(4000) not null,
                     RDF$STC_obj varchar2(4000) not null,
                     RDF$STC_sub_ext varchar2(64),
                     RDF$STC_pred_ext varchar2(64),
                     RDF$STC_obj_ext varchar2(64),
                     RDF$STC_canon_ext varchar2(64)
);

You must grant SELECT privilege and UPDATE privilege on the last four required columns (with names ending with _collision_ext) in the staging table to user MDSYS. You must also grant INSERT privilege on the application table to user MDSYS.

You can use the SQL*Loader utility to parse and load semantic data into a staging table. (If you installed the demo files from the Oracle Database Examples media, a sample control file is available at $ORACLE_HOME/md/demo/network/rdf_demos/bulkload.ctl. You can modify and use this file.)

Objects longer than 4000 bytes cannot be loaded. If you use the sample SQL*Loader control file, triples (rows) containing such long values will be automatically rejected and stored in a SQL*Loader "bad" file.

However, triples containing object values longer than 4000 bytes can beloaded using the following approach:

1. Use the SEM_APIS.BULK_LOAD_FROM_STAGING_TABLE procedure to load all rows that can be stored in the staging table.

2. Load the remaining rows (that is, the rejected rows when using SQL*Loader with the sample control file) from an N-Triple format file, as described in Section 1.7.2.

1.7.2 Batch Loading Semantic Data Using the Java API

You can perform a batch load operation using the Java class oracle.spatial.rdf.client.BatchLoader, which is packaged in <ORACLE_HOME>/md/jlib/sdordf.jar. Before performing a batch load operation, ensure that the following are true:

• The semantic data is in N-Triple format. (Several tools are available for converting RDF/XML to N-Triple format; see the Oracle Technology Network or perform a Web search for information about RDF/XML to N-Triple conversion.)

• Oracle Database Release 11, with Oracle Spatial, is installed.

• A semantic technologies network, an application table, and its corresponding semantic model have been created in the database.

• The CLASSPATH definition includes ojdbc5.jar.

• You are using JDK version 1.5 or later. (You can use the Java version packaged under <ORACLE_HOME>/jdk/bin.)

To run the oracle.spatial.rdf.client.BatchLoader class, use a command (on a single command line) in the following general form (replacing the sample example database connection information with your own connection information).

• Linux systems:

  java -Ddb.user=scott -Ddb.password=tiger -Ddb.host=127.0.0.1 -Ddb.port=1522 -Ddb.sid=orcl -classpath ${ORACLE_HOME}/md/jlib/sdordf.jar:${ORACLE_HOME}/jdbc/lib/ojdbc5.jar oracle.spatial.rdf.client.BatchLoader <N-TripleFile> <tablename> <tablespaceName> <modelName>
  
  

• Windows systems:

  java -Ddb.user=scott -Ddb.password=tiger -Ddb.host=127.0.0.1 -Ddb.port=1522 -Ddb.sid=orcl -classpath %ORACLE_HOME%\md\jlib\sdordf.jar;%ORACLE_HOME%\jdbc\lib\ojdbc5.jar oracle.spatial.rdf.client.BatchLoader <N-TripleFile> <tablename> <tablespaceName> <modelName>
  
  

By default, BatchLoader assumes there are at least two columns, a column named ID of type NUMBER and a column named TRIPLE of type SDO_RDF_TRIPLE_S, in the user's application table. However, you can override the default names by using the JVM properties -DidColumn=<idColumnName> and -DtripleColumn=<tripleColumnName>. Note that the ID column is not required; and to prevent BatchLoader from generating a sequence-like identifier in the ID column for each triple inserted, specify the JVM property -DjustTriple=true.

If the application table is not empty and if you want the batch loading to be done in append mode, specify an additional JVM property: -Dappend=true. Moreover, in append mode you might want to choose a different starting value for ID column in user's application table, and to accomplish this you can add the JVM property -DstartID=<startingIntegerValue> to the command line. By default, the ID column starts at 1 and is increased sequentially as new triples are inserted into the application table.

To skip the first n triples in <N-TripleFile>, add the JVM property -Dskip=<numberOfTriplesSkipped> to the command line.

To load an N-Triple file with a character set different from the default, specify the JVM property -Dcharset=<charsetName>. For example, -Dcharset="UTF-8" will recognize UTF-8 encoding. However, for UTF-8 characters to be stored properly in the N-Triple file, the Oracle database must be configured to use a corresponding universal character set, such as AL32UTF8.

The BatchLoader class supports loading an N-Triple file in compressed format. If the <N-TripleFile> has a file extension of .zip or .jar, the file will be uncompressed and loaded at the same time.

1.7.3 Loading Semantic Data Using INSERT Statements

To load semantic data using INSERT statements, the data should be encoded using < > (angle brackets) for URIs, _: (underscore colon) for blank nodes, and " " (quotation marks) for literals. Spaces are not allowed in URIs or blank nodes. Use the SDO_RDF_TRIPLE_S constructor to insert the data, as described in Section 1.5.1.

The following example includes statements with URIs, a blank node (the model_id for nsu is 4), a literal, a literal with a language tag, and a typed literal:

INSERT INTO nsu_data VALUES (SDO_RDF_TRIPLE_S('nsu', '<http://www.nature.com/nsu/rss.rdf>',
  '<http://purl.org/rss/1.0/title>', '"Nature''s Science Update"'));
INSERT INTO nsu_data VALUES (SDO_RDF_TRIPLE_S('nsu', '_:BNSEQN1001A',
  '<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>', 
  '<http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq>', 4));
INSERT INTO nsu_data VALUES (SDO_RDF_TRIPLE_S('nsu',
  '<http://www.nature.com/cgi-taf/dynapage.taf?file=/nature/journal/v428/n6978/index.html>',
  '<http://purl.org/dc/elements/1.1/language>', '"EnglishÓ@en-GB'));
INSERT INTO nature VALUES (SDO_RDF_TRIPLE_S('nsu', '<http://dx.doi.org/10.1038/428004b>',
  '<http://purl.org/dc/elements/1.1/date>', '"2004-03-04"^^xsd:date'));

To convert semantic XML data to INSERT statements, you can edit the sample rss2insert.xsl XSLT file to convert all the features in the semantic data XML file. The blank node constructor is used to insert statements with blank nodes. After editing the XSLT, download the Xalan XSLT processor (http://xml.apache.org/xalan) and follow the installation instructions. To convert a semantic data XML file to INSERT statements using your edited version of the rss2insert.xsl file, use a command in the following format:

java org.apache.xalan.xslt.Process –in input.rdf -xsl rss2insert.xsl –out output.nt

1.7.4 Exporting Semantic Data

To output semantic data to a file in N-Triple format, use the NTripleConverter Java class. The NDM2NTriple(String, int) method exports all the triples stored for the specified model.

For information about using the NTriple converter class, see the README.txt file in the sdordf_converter.zip file, which you can download from the Oracle Technology Network.

1.9.1 Example: Journal Article Information

This section presents a simplified PL/SQL example of model for statements about journal articles. Example 1-9 contains descriptive comments, refer to concepts that are explained in this chapter, and uses functions and procedures documented in Chapter 3.

-- Basic steps:
-- After you have connected as a privileged user and called 
-- SEM_APIS.CREATE_RDF_NETWORK to add RDF support,
-- connect as a regular database user and do the following.
-- 1. For each desired model, create a table to hold its data.
-- 2. For each model, create a model (SEM_APIS.CREATE_RDF_MODEL).
-- 3. For each table to hold semantic data, insert data into the table.
-- 4. Use various subprograms and consructors.
 
-- Create the table to hold data for the model.
CREATE TABLE articles_rdf_data (id NUMBER, triple SDO_RDF_TRIPLE_S);
 
-- Create the model.
EXECUTE SEM_APIS.CREATE_RDF_MODEL('articles', 'articles_rdf_data', 'triple');
 
-- Information to be stored about some fictitious articles:
-- Article1, titled "All about XYZ" and written by Jane Smith, refers 
--   to Article2 and Article3.
-- Article2, titled "A review of ABC" and written by Joe Bloggs, 
--   refers to Article3.
-- Seven SQL statements to store the information. In each statement:
-- Each article is referred to by its complete URI The URIs in
--   this example are fictitious, although they are in the general 
--   domain of the journal Nature (http://www.nature.com/nature/).
-- Each property is referred to by the URL for its definition, as 
--   created by the Dublin Core Metadata Initiative.
 
-- Insert rows into the table.
 
-- Article1 has the title "All about XYZ".
INSERT INTO articles_rdf_data VALUES (1,
  SDO_RDF_TRIPLE_S ('articles','http://www.nature.com/nature/Article1',
    'http://purl.org/dc/elements/1.1/title','All about XYZ'));
 
-- Article1 was created (written) by Jane Smith.
INSERT INTO articles_rdf_data VALUES (2,
  SDO_RDF_TRIPLE_S ('articles','http://www.nature.com/nature/Article1',
    'http://purl.org/dc/elements/1.1/creator',
    'Jane Smith'));
 
-- Article1 references (refers to) Article2.
INSERT INTO articles_rdf_data VALUES (3,
  SDO_RDF_TRIPLE_S ('articles',
    'http://www.nature.com/nature/Article1',
    'http://purl.org/dc/terms/references',
    'http://www.nature.com/nature/Article2'));
 
-- Article1 references (refers to) Article3.
INSERT INTO articles_rdf_data VALUES (4,
  SDO_RDF_TRIPLE_S ('articles',
    'http://www.nature.com/nature/Article1',
    'http://purl.org/dc/terms/references',
    'http://www.nature.com/nature/Article3'));
 
-- Article2 has the title "A review of ABC".
INSERT INTO articles_rdf_data VALUES (5,
  SDO_RDF_TRIPLE_S ('articles',
    'http://www.nature.com/nature/Article2',
    'http://purl.org/dc/elements/1.1/title',
    'A review of ABC'));
 
-- Article2 was created (written) by Joe Bloggs.
INSERT INTO articles_rdf_data VALUES (6,
  SDO_RDF_TRIPLE_S ('articles',
    'http://www.nature.com/nature/Article2',
    'http://purl.org/dc/elements/1.1/creator',
    'Joe Bloggs'));
 
-- Article2 references (refers to) Article3.
INSERT INTO articles_rdf_data VALUES (7,
  SDO_RDF_TRIPLE_S ('articles',
    'http://www.nature.com/nature/Article2',
    'http://purl.org/dc/terms/references',
    'http://www.nature.com/nature/Article3'));
 
COMMIT;
 
-- Query semantic data.
 
SELECT SEM_APIS.GET_MODEL_ID('articles') AS model_id FROM DUAL;

SELECT SEM_APIS.GET_TRIPLE_ID(
  'articles',
  'http://www.nature.com/nature/Article2',
  'http://purl.org/dc/terms/references',
  'http://www.nature.com/nature/Article3') AS RDF_triple_id FROM DUAL;
 
SELECT SEM_APIS.IS_TRIPLE(
  'articles',
  'http://www.nature.com/nature/Article2',
  'http://purl.org/dc/terms/references',
  'http://www.nature.com/nature/Article3') AS is_triple FROM DUAL;
 
-- Use SDO_RDF_TRIPLE_S member functions in queries.
 
SELECT a.triple.GET_TRIPLE() AS triple 
  FROM articles_rdf_data a WHERE a.id = 1;
SELECT a.triple.GET_SUBJECT() AS subject 
  FROM articles_rdf_data a WHERE a.id = 1;
SELECT a.triple.GET_PROPERTY() AS property 
  FROM articles_rdf_data a WHERE a.id = 1;
SELECT a.triple.GET_OBJECT() AS object 
  FROM articles_rdf_data a WHERE a.id = 1;

1.9.2 Example: Family Information

This section presents a simplified PL/SQL example of a model for statements about family tree (genealogy) information. Example 1-9 contains descriptive comments, refer to concepts that are explained in this chapter, and uses functions and procedures documented in Chapter 3.

The family relationships in this example reflect the family tree shown in Figure 1-3. This figure also shows some of the information directly stated in the example: Cathy is the sister of Jack, Jack and Tom are male, and Cindy is female.

Figure 1-3 Family Tree for RDF Example

Description of "Figure 1-3 Family Tree for RDF Example"

-- Basic steps:
-- After you have connected as a privileged user and called 
-- SEM_APIS.CREATE_RDF_NETWORK to enable RDF support,
-- connect as a regular database user and do the following.
-- 1. For each desired model, create a table to hold its data.
-- 2. For each model, create a model (SEM_APIS.CREATE_RDF_MODEL).
-- 3. For each table to hold semantic data, insert data into the table.
-- 4. Use various subprograms and constructors.
 
-- Create the table to hold data for the model.
CREATE TABLE family_rdf_data (id NUMBER, triple SDO_RDF_TRIPLE_S);
 
-- Create the model.
execute SEM_APIS.create_rdf_model('family', 'family_rdf_data', 'triple');
 
-- Insert rows into the table. These express the following information:
-----------------
-- John and Janice have two children, Suzie and Matt.
-- Matt married Martha, and they have two children:
--   Tom (male, height 5.75) and Cindy (female, height 06.00).
-- Suzie married Sammy, and they have two children:
--   Cathy (height 5.8) and Jack (male, height 6).
 
-- Person is a class that has two subslasses: Male and Female.
-- parentOf is a property that has two subproperties: fatherOf and motherOf.
-- siblingOf is a property that has two subproperties: brotherOf and sisterOf.
-- The domain of the fatherOf and brotherOf properties is Male.
-- The domain of the motherOf and sisterOf properties is Female.
------------------------
 
-- John is the father of Suzie.
INSERT INTO family_rdf_data VALUES (1, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/John', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Suzie'));
 
-- John is the father of Matt.
INSERT INTO family_rdf_data VALUES (2, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/John', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Matt'));
 
-- Janice is the mother of Suzie.
INSERT INTO family_rdf_data VALUES (3, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Janice', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Suzie'));
 
-- Janice is the mother of Matt.
INSERT INTO family_rdf_data VALUES (4, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Janice', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Matt'));
 
-- Sammy is the father of Cathy.
INSERT INTO family_rdf_data VALUES (5, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Sammy', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Cathy'));
 
-- Sammy is the father of Jack.
INSERT INTO family_rdf_data VALUES (6, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Sammy', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Jack'));
 
-- Suzie is the mother of Cathy.
INSERT INTO family_rdf_data VALUES (7, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Suzie', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Cathy'));
 
-- Suzie is the mother of Jack.
INSERT INTO family_rdf_data VALUES (8, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Suzie', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Jack'));
 
-- Matt is the father of Tom.
INSERT INTO family_rdf_data VALUES (9, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Matt', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Tom'));
 
-- Matt is the father of Cindy
INSERT INTO family_rdf_data VALUES (10, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Matt', 
'http://www.example.org/family/fatherOf', 
'http://www.example.org/family/Cindy'));
 
-- Martha is the mother of Tom.
INSERT INTO family_rdf_data VALUES (11, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Martha', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Tom'));
 
-- Martha is the mother of Cindy. 
INSERT INTO family_rdf_data VALUES (12, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Martha', 
'http://www.example.org/family/motherOf', 
'http://www.example.org/family/Cindy'));
 
-- Cathy is the sister of Jack.
INSERT INTO family_rdf_data VALUES (13, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Cathy', 
'http://www.example.org/family/sisterOf', 
'http://www.example.org/family/Jack'));
 
-- Jack is male.
INSERT INTO family_rdf_data VALUES (14, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Jack', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.example.org/family/Male'));
 
-- Tom is male.
INSERT INTO family_rdf_data VALUES (15, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Tom', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.example.org/family/Male'));
 
-- Cindy is female.
INSERT INTO family_rdf_data VALUES (16, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Cindy', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.example.org/family/Female'));
 
-- Person is a class.
INSERT INTO family_rdf_data VALUES (17, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Person', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.w3.org/2000/01/rdf-schema#Class'));
 
-- Male is a subclass of Person.
INSERT INTO family_rdf_data VALUES (18, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Male', 
'http://www.w3.org/2000/01/rdf-schema#subClassOf',
'http://www.example.org/family/Person'));
 
-- Female is a subclass of Person. 
INSERT INTO family_rdf_data VALUES (19, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Female', 
'http://www.w3.org/2000/01/rdf-schema#subClassOf',
'http://www.example.org/family/Person'));
 
-- siblingOf is a property.
INSERT INTO family_rdf_data VALUES (20, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/siblingOf', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.w3.org/1999/02/22-rdf-syntax-ns#Property'));
 
-- parentOf is a property.
INSERT INTO family_rdf_data VALUES (21, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/parentOf', 
'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
'http://www.w3.org/1999/02/22-rdf-syntax-ns#Property'));
 
-- brotherOf is a subproperty of siblingOf.
INSERT INTO family_rdf_data VALUES (22, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/brotherOf', 
'http://www.w3.org/2000/01/rdf-schema#subPropertyOf',
'http://www.example.org/family/siblingOf'));
 
-- sisterOf is a subproperty of siblingOf.
INSERT INTO family_rdf_data VALUES (23, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/sisterOf', 
'http://www.w3.org/2000/01/rdf-schema#subPropertyOf',
'http://www.example.org/family/siblingOf'));
 
-- A brother is male.
INSERT INTO family_rdf_data VALUES (24, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/brotherOf', 
'http://www.w3.org/2000/01/rdf-schema#domain',
'http://www.example.org/family/Male'));
 
-- A sister is female.
INSERT INTO family_rdf_data VALUES (25, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/sisterOf', 
'http://www.w3.org/2000/01/rdf-schema#domain',
'http://www.example.org/family/Female'));
 
-- fatherOf is a subproperty of parentOf.
INSERT INTO family_rdf_data VALUES (26, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/fatherOf', 
'http://www.w3.org/2000/01/rdf-schema#subPropertyOf',
'http://www.example.org/family/parentOf'));
 
-- motherOf is a subproperty of parentOf.
INSERT INTO family_rdf_data VALUES (27, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/motherOf', 
'http://www.w3.org/2000/01/rdf-schema#subPropertyOf',
'http://www.example.org/family/parentOf'));
 
-- A father is male.
INSERT INTO family_rdf_data VALUES (28, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/fatherOf', 
'http://www.w3.org/2000/01/rdf-schema#domain',
'http://www.example.org/family/Male'));
 
-- A mother is female.
INSERT INTO family_rdf_data VALUES (29, 
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/motherOf', 
'http://www.w3.org/2000/01/rdf-schema#domain',
'http://www.example.org/family/Female'));
 
-- Use SET ESCAPE OFF to prevent the caret (^) from being
-- interpreted as an escape character. Two carets (^^) are
-- used to represent typed literals.
SET ESCAPE OFF;
 
-- Cathy's height is 5.8 (decimal).
INSERT INTO family_rdf_data VALUES (30,
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Cathy', 
'http://www.example.org/family/height',
'"5.8"^^xsd:decimal'));
 
-- Jack's height is 6 (integer).
INSERT INTO family_rdf_data VALUES (31,
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Jack', 
'http://www.example.org/family/height',
'"6"^^xsd:integer'));
 
-- Tom's height is 05.75 (decimal).
INSERT INTO family_rdf_data VALUES (32,
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Tom', 
'http://www.example.org/family/height',
'"05.75"^^xsd:decimal'));
 
-- Cindy's height is 06.00 (decimal).
INSERT INTO family_rdf_data VALUES (33,
SDO_RDF_TRIPLE_S('family', 
'http://www.example.org/family/Cindy', 
'http://www.example.org/family/height',
'"06.00"^^xsd:decimal'));
 
COMMIT;
 
-- RDFS inferencing in the family model
BEGIN
  SEM_APIS.CREATE_RULES_INDEX(
    'rdfs_rix_family',
    SEM_Models('family'),
    SEM_Rulebases('RDFS'));
END;
/
 
-- Select all males from the family model, without inferencing.
SELECT m
  FROM TABLE(SEM_MATCH(
    '(?m rdf:type :Male)',
    SEM_Models('family'),
    null,
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')),
    null));
 
-- Select all males from the family model, with RDFS inferencing.
SELECT m
  FROM TABLE(SEM_MATCH(
    '(?m rdf:type :Male)',
    SEM_Models('family'),
    SDO_RDF_Rulebases('RDFS'), 
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')),
    null));
 
-- General inferencing in the family model
 
EXECUTE SEM_APIS.CREATE_RULEBASE('family_rb');
 
INSERT INTO mdsys.semr_family_rb VALUES(
  'grandparent_rule',
  '(?x :parentOf ?y) (?y :parentOf ?z)',
  NULL,
  '(?x :grandParentOf ?z)', 
  SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')));
 
COMMIT;
 
-- Because a new rulebase has been created, and it will be used in the
-- rules index, drop the preceding rules index and then re-create it.
EXECUTE SEM_APIS.DROP_RULES_INDEX ('rdfs_rix_family');
 
-- Re-create the rules index.
BEGIN
  SEM_APIS.CREATE_RULES_INDEX(
    'rdfs_rix_family',
    SEM_Models('family'),
    SEM_Rulebases('RDFS','family_rb'));
END;
/
 
-- Select all grandfathers and their grandchildren from the family model, 
-- without inferencing. (With no inferencing, no results are returned.)
SELECT x grandfather, y grandchild
  FROM TABLE(SEM_MATCH(
    '(?x :grandParentOf ?y) (?x rdf:type :Male)',
    SEM_Models('family'),
    null, 
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')),
    null));
 
-- Select all grandfathers and their grandchildren from the family model.
-- Use inferencing from both the RDFS and family_rb rulebases.
SELECT x grandfather, y grandchild
  FROM TABLE(SEM_MATCH(
    '(?x :grandParentOf ?y) (?x rdf:type :Male)',
    SEM_Models('family'),
    SEM_Rulebases('RDFS','family_rb'), 
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')),
    null));
 
-- Set up to find grandfathers of tall (>= 6) grandchildren
-- from the family model, with RDFS inferencing and
-- inferencing using the "family_rb" rulebase.
 
UPDATE mdsys.semr_family_rb SET
  antecedents = '(?x :parentOf ?y) (?y :parentOf ?z) (?z :height ?h)',
  filter = '(h >= 6)',
  aliases = SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/'))
WHERE rule_name = 'GRANDPARENT_RULE';
 
-- Because the rulebase has been updated, drop the preceding rules index, 
-- and then re-create it.
EXECUTE SEM_APIS.DROP_RULES_INDEX ('rdfs_rix_family');
 
-- Re-create the rules index.
BEGIN
  SEM_APIS.CREATE_RULES_INDEX(
    'rdfs_rix_family',
    SEM_Models('family'),
    SEM_Rulebases('RDFS','family_rb'));
END;
/
 
-- Find the rules index that was just created (that is, the
-- one based on the specified model and rulebases).
SELECT SEM_APIS.LOOKUP_RULES_INDEX(SEM_MODELS('family'),
  SEM_RULEBASES('RDFS','family_rb')) AS lookup_rules_index FROM DUAL;
 
-- Select grandfathers of tall (>= 6) grandchildren, and their
-- tall grandchildren.
SELECT x grandfather, y grandchild
  FROM TABLE(SEM_MATCH(
    '(?x :grandParentOf ?y) (?x rdf:type :Male)',
    SEM_Models('family'),
    SEM_RuleBases('RDFS','family_rb'), 
    SEM_ALIASES(SEM_ALIAS('','http://www.example.org/family/')), 
    null));