Handling null values in SQL queries over object-oriented data

Claim 1

A method of handling null values in a query having a subquery, the query being performed by a computer to retrieve object-oriented data from a database stored in an electronic storage device connected to the computer, the method comprising the steps of: (a) iteratively eliminating, in the computer, negation in each predicate of the query by applying logical equivalence rules; and (b) iteratively performing, in the computer, null protection on each predicate of the query after eliminating negation, to ensure that null values are checked when attempting to retrieve the object-oriented data from the electronic storage device coupled to the computer within a two-valued logic environment.

Claim 2

A method of handling null values in a query having a subquery, the query being performed by a computer to retrieve object-oriented data from a database stored in an electronic storage device connected to the computer, the method comprising the steps of: (a) iteratively eliminating, in the computer, negation in each predicate of the query by applying logical equivalence rules; and (b) iteratively performing, in the computer, null protection on each predicate of the query after eliminating negation, to ensure that null values are checked when attempting to retrieve the object-oriented data from the electronic storage device coupled to the computer within a two-valued logic environment.

Claim 7

An apparatus for handling null values in a query having a subquery, comprising: a computer with an electronic storage device connected thereto, the electronic storage device storing object-oriented data; means for executing the query in the computer to retrieve the object-oriented data from the electronic storage device; means, performed by the computer, for iteratively eliminating negation in each predicate of the query by applying logical equivalence rules; and means, performed by the computer, for iteratively performing null protection on each predicate of the query after eliminating negation, to ensure that null values are checked when attempting to retrieve the object-oriented data from the electronic storage device coupled to the computer within a two-valued logic environment.

Claim 8

An apparatus for handling null values in a query having a subquery, comprising: a computer with an electronic storage device connected thereto, the electronic storage device storing object-oriented data; means for executing the query in the computer to retrieve the object-oriented data from the electronic storage device; means, performed by the computer, for iteratively eliminating negation in each predicate of the query by applying logical equivalence rules; and means, performed by the computer, for iteratively performing null protection on each predicate of the query after eliminating negation, to ensure that null values are checked when attempting to retrieve the object-oriented data from the electronic storage device coupled to the computer within a two-valued logic environment.

Claim 20

A method for processing a query in a computer system, comprising the steps of: providing, in a two-valued logic system where NULL values are unsupported, a tri-valued logic interpretation, by a query engine, of predicates involving subqueries having a capability to have NULL pointers; and protecting the query engine processing the query from abnormal termination due to dereferencing one of the NULL pointers.

Claim 21

A method for processing a query in a computer system, comprising the steps of: providing, in a two-valued logic system where NULL values are unsupported, a tri-valued logic interpretation, by a query engine, of predicates involving subqueries having a capability to have NULL pointers; and protecting the query engine processing the query from abnormal termination due to dereferencing one of the NULL pointers.

Claim 22

A method for processing queries in a computer system, comprising the steps of: processing, by a two-valued logic system which is not supportive of NULL values in an environment having NULL pointers, a predicate having a subquery by transforming the predicate by: employing a technique to handle each occurrence of a negative predicate, if any, as a positive predicate; transforming a quantified subquery, if any, into an existential form; applying null tests, by the query system, to each resulting predicate; and interpreting the semantics of the NULL tested resulting predicate such that a presence of a NULL pointer or a NULL value is handled in a same way as if the predicate evaluated to False by not returning a result; wherein the two-valued logic system simulates tri-valued logic and the query system does not terminate abnormally if a NULL pointer is traversed.

Claim 23

A method for processing queries in a computer system, comprising the steps of: processing, by a two-valued logic system which is not supportive of NULL values in an environment having NULL pointers, a predicate having a subquery by transforming the predicate by: employing a technique to handle each occurrence of a negative predicate, if any, as a positive predicate; transforming a quantified subquery, if any, into an existential form; applying null tests, by the query system, to each resulting predicate; and interpreting the semantics of the NULL tested resulting predicate such that a presence of a NULL pointer or a NULL value is handled in a same way as if the predicate evaluated to False by not returning a result; wherein the two-valued logic system simulates tri-valued logic and the query system does not terminate abnormally if a NULL pointer is traversed.

Claim 31

A method for processing a query having a predicate with a subquery in a computer system, comprising the steps of: using a two-valued logic system to process the query, the query being capable of having NULL values; reducing each predicate in the query from a negative predicate to a logically equivalent positive predicate; applying NULL pointer testing predicates to each positive predicate to ensure that path expression traversal does not extend beyond NULL pointers; and interpreting the NULL tested positive predicates that include NULL pointers similarly to a False value of the predicate by not being included in the result.

Claim 32

A method for processing a query having a predicate with a subquery in a computer system, comprising the steps of: using a two-valued logic system to process the query, the query being capable of having NULL values; reducing each predicate in the query from a negative predicate to a logically equivalent positive predicate; applying NULL pointer testing predicates to each positive predicate to ensure that path expression traversal does not extend beyond NULL pointers; and interpreting the NULL tested positive predicates that include NULL pointers similarly to a False value of the predicate by not being included in the result.

Claim 34

A method for processing a query in a computer system, comprising the steps of: transforming a predicate having a subquery into a logically equivalent predicate; checking for nullness, in query systems that support subqueries and in an environment where NULL values are unsupported, each attribute (m 1 through m n ) along each path expression p having a form q.m 1 ..m 2 .., . . . , ..m n where m 1 , . . . , m n can be NULL pointers within the transformed predicate; interpretating, by a two-valued logic system, the check for nullness of the transformed predicate in a way that supports tri-valued logic; and continuing to resolve the path after the check for nullness; wherein a presence of a NULL pointer in the transformed predicate is handled in a same way as a FALSE value of the predicate having a subquery by not returning a result and the query engine processing the query is protected from abnormal termination due to dereferencing the NULL pointer.

Claim 35

A method for processing a query in a computer system, comprising the steps of: transforming a predicate having a subquery into a logically equivalent predicate; checking for nullness, in query systems that support subqueries and in an environment where NULL values are unsupported, each attribute (m 1 through m n ) along each path expression p having a form q.m 1 ..m 2 .., . . . , ..m n where m 1 , . . . , m n can be NULL pointers within the transformed predicate; interpretating, by a two-valued logic system, the check for nullness of the transformed predicate in a way that supports tri-valued logic; and continuing to resolve the path after the check for nullness; wherein a presence of a NULL pointer in the transformed predicate is handled in a same way as a FALSE value of the predicate having a subquery by not returning a result and the query engine processing the query is protected from abnormal termination due to dereferencing the NULL pointer.

Claim 36

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NULL predicate to a path expression in the query; and interpreting a semantic of the IS NULL as being TRUE if the path expression has a node which is a NULL pointer.

Claim 37

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NULL predicate to a path expression in the query; and interpreting a semantic of the IS NULL as being TRUE if the path expression has a node which is a NULL pointer.

Claim 38

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NULL predicate to a path expression in the query; and interpreting a semantic of the IS NULL as being FALSE if the path expression does not have a node which is a NULL pointer.

Claim 39

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NULL predicate to a path expression in the query; and interpreting a semantic of the IS NULL as being FALSE if the path expression does not have a node which is a NULL pointer.

Claim 40

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NOT NULL predicate to a path expression in the query; and interpreting a semantic of the IS NOT NULL as being FALSE if the path expression has a node which is a NULL pointer.

Claim 41

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NOT NULL predicate to a path expression in the query; and interpreting a semantic of the IS NOT NULL as being FALSE if the path expression has a node which is a NULL pointer.

Claim 42

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NOT NULL predicate to a path expression in the query; and interpreting a semantic of the IS NOT NULL as being TRUE if the path expression does not have a node which is a NULL pointer.

Claim 43

A method for processing a query in a computer system, comprising the steps of: applying, in an environment having NULL pointers and where NULL values are unsupported, an IS NOT NULL predicate to a path expression in the query; and interpreting a semantic of the IS NOT NULL as being TRUE if the path expression does not have a node which is a NULL pointer.

Claim 44

The method of claims 29 or 31, further comprising the step of continuing to process the query without an abnormal termination of a query engine as a result of a traversal of the NULL pointer.

Claim 45

The method of claims 29, 30, 31, or 32, wherein the environment is an object-oriented database environment.

Claim 46

The method of claims 29, 30, 31, or 32, wherein the environment is an object-oriented system.

Claim 47

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, the query having a basic predicate with a subquery; and interpreting the predicate as NULL if an operand is NULL or if the subquery returns an empty result.

Claim 48

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, the query having a basic predicate with a subquery; and interpreting the predicate as NULL if an operand is NULL or if the subquery returns an empty result.

Claim 49

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, the query having a predicate with a universal quantified subquery; and interpreting the predicate as NULL if a relationship is not FALSE for any values returned by the subquery and at least one comparison is unknown because of a NULL value.

Claim 50

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, the query having a predicate with a universal quantified subquery; and interpreting the predicate as NULL if a relationship is not FALSE for any values returned by the subquery and at least one comparison is unknown because of a NULL value.

Claim 51

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, having a predicate with an existential quantified subquery; and interpreting the predicate as NULL if a specified relationship is not TRUE for any values returned by the subquery and at least one comparison is unknown because of a NULL value.

Claim 52

A method for processing a query in a computer system, comprising the steps of: processing the query, in an environment where NULL values are unsupported, having a predicate with an existential quantified subquery; and interpreting the predicate as NULL if a specified relationship is not TRUE for any values returned by the subquery and at least one comparison is unknown because of a NULL value.

Claim 53

A method for processing queries in a computer system, comprising the steps of: processing, in an environment where NULL values are unsupported, a predicate having a path expression by: (a) transforming each occurrence, if any, of a negative predicate into a positive predicate; and (b) applying null protection transformations to each positive predicate by: <(i) transforming a positive expression p 1 r k as p 1 r k→q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r k; and (ii) transforming a positive expression p 1 r p 2 as p 1 r p 2 →q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and . . . and q 2 .m 1 .., . . . , ..m m-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m , wherein: p 1 is a path expression of the form q 1 .m 1 ..m 2 .., . . . , ..m n in which attributes m 1 , . . . , m n-1 can be NULL pointers, r is a relational operator among {=, ≠, <, ≦, >, ≧}, k is a constant, and p 2 is a path expression of the form q 2 .m 1 ..m 2 .., . . . , ..m n where m 1 , . . . ,m n-1 are attributes that can be NULL pointers.

Claim 54

A method for processing queries in a computer system, comprising the steps of: processing, in an environment where NULL values are unsupported, a predicate having a path expression by: (a) transforming each occurrence, if any, of a negative predicate into a positive predicate; and (b) applying null protection transformations to each positive predicate by: <(i) transforming a positive expression p 1 r k as p 1 r k→q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r k; and (ii) transforming a positive expression p 1 r p 2 as p 1 r p 2 →q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and . . . and q 2 .m 1 .., . . . , ..m m-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m , wherein: p 1 is a path expression of the form q 1 .m 1 ..m 2 .., . . . , ..m n in which attributes m 1 , . . . , m n-1 can be NULL pointers, r is a relational operator among {=, ≠, <, ≦, >, ≧}, k is a constant, and p 2 is a path expression of the form q 2 .m 1 ..m 2 .., . . . , ..m n where m 1 , . . . ,m n-1 are attributes that can be NULL pointers.

Claim 55

A method for processing queries in a computer system, comprising the steps of: processing, in an environment where NULL values are unsupported, a predicate having a subquery by: (a) employing a technique to handle each occurrence, if any, of a negative predicate as a positive predicate; (b) converting quantified subqueries into existential subqueries and pushing a created predicate into a body of the subquery; (c) applying null protection transformations to each resulting predicate, except a "not exists Q" resulting from the conversion step (b), by: (i) transforming an expression p 1 r k as p 1 r k→q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r k; (ii) transforming an expression p 1 r p 2 as p 1 r p 2 →q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n ≠NULL and q 2 .m 1 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and . . . and q 2 .m 1 .., . . . , ..m m-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m ; and (d) applying a following applicable null protection transformation to a predicate, if any, having the form "not exists Q", if the form "not exists Q" is a result of the conversion of quantified subqueries into existential subqueries of step (b): (i) (p 1 r k)→(q 1 .m 1 =NULL or q 1 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m n-1 =NULL or q 1 .m 1 .., . . . , ..m n r k); (ii) (p 1 r p 2 )→(q 1 .m 1 =NULL or q 1 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m n-1 =NULL or q 2 .m 1 =NULL or q 2 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m m-1 =NULL or q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m ), wherein: p 1 is a path expression of the form q 1 .m 1 ..m 2 .., . . . , ..m n in which attributes m 1 , . . . , m n-1 can be NULL pointers, r is a relational operator among {=, ≠, <, ≦, >, ≧}, k is a constant, and p 2 is a path expression of the form q 2 .m 1 ..m 2 .., . . . , ..m n where m 1 , . . . ,m n-1 are attributes that can be NULL pointers.

Claim 56

A method for processing queries in a computer system, comprising the steps of: processing, in an environment where NULL values are unsupported, a predicate having a subquery by: (a) employing a technique to handle each occurrence, if any, of a negative predicate as a positive predicate; (b) converting quantified subqueries into existential subqueries and pushing a created predicate into a body of the subquery; (c) applying null protection transformations to each resulting predicate, except a "not exists Q" resulting from the conversion step (b), by: (i) transforming an expression p 1 r k as p 1 r k→q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r k; (ii) transforming an expression p 1 r p 2 as p 1 r p 2 →q 1 .m 1 ≠NULL and q 1 .m 1 ..m 2 ≠NULL and . . . and q 1 .m 1 .., . . . , ..m n ≠NULL and q 2 .m 1 ≠NULL and q 2 .m 1 ..m 2 ≠NULL and . . . and q 2 .m 1 .., . . . , ..m m-1 ≠NULL and q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m ; and (d) applying a following applicable null protection transformation to a predicate, if any, having the form "not exists Q", if the form "not exists Q" is a result of the conversion of quantified subqueries into existential subqueries of step (b): (i) (p 1 r k)→(q 1 .m 1 =NULL or q 1 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m n-1 =NULL or q 1 .m 1 .., . . . , ..m n r k); (ii) (p 1 r p 2 )→(q 1 .m 1 =NULL or q 1 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m n-1 =NULL or q 2 .m 1 =NULL or q 2 .m 1 ..m 2 =NULL or . . . or q 1 .m 1 .., . . . , ..m m-1 =NULL or q 1 .m 1 .., . . . , ..m n r q 2 .m 1 .., . . . , ..m m ), wherein: p 1 is a path expression of the form q 1 .m 1 ..m 2 .., . . . , ..m n in which attributes m 1 , . . . , m n-1 can be NULL pointers, r is a relational operator among {=, ≠, <, ≦, >, ≧}, k is a constant, and p 2 is a path expression of the form q 2 .m 1 ..m 2 .., . . . , ..m n where m 1 , . . . ,m n-1 are attributes that can be NULL pointers.

Claim 59

A method for processing a query having a predicate with a subquery in a computer system, comprising the steps of: using a two-valued logic system to process the query, the query being capable of having NULL values; reducing each predicate in the query from a negative predicate to a positive predicate; and applying NULL pointer testing predicates to each predicate to ensure that path expression traversal does not extend beyond NULL pointers and to interpret predicates that include NULL pointers such that a NULL or False truth value are handled similarly by not being included in the result.

Claim 60

A method for processing a query having a predicate with a subquery in a computer system, comprising the steps of: using a two-valued logic system to process the query, the query being capable of having NULL values; reducing each predicate in the query from a negative predicate to a positive predicate; and applying NULL pointer testing predicates to each predicate to ensure that path expression traversal does not extend beyond NULL pointers and to interpret predicates that include NULL pointers such that a NULL or False truth value are handled similarly by not being included in the result.