Fuzzy Querying Capability at Core of a RDBMS - Advanced Database Query Systems - page 175

Box 8.

typedef struct A_FuzzyPred {
NodeTag type;

char *pred; // predicate name

int minfp; // support's left bound

int modminfp;

int core1; // core's left bound (included)

int modcore1;

int core2; // core's right bound (included)

int modcore2;

int maxfp; // support's right bound

int modmaxfp;

int typefp; // shape 1(trapz.) 2(increases) 3(decreases)

int modtypefp;

unsigned int vno; // table number

int vattno; // relative attribute number

Oid rorigtab;

Oid rorigcol;

List *compfplist; // compare fuzzy predicate list

List *modcompfplist;

char *exprfp; // fuzzy expression

char *disd; // discrete domain

bool hasfm; // has fuzzy modificator

char *fuzzymod; // fuzzy modificator

int Mtype; // modificator type

int Mpower; // modificator power

int normType;

int vtype;

} A_FuzzyPred;

As we can see in Figure 4, the parser module generates a parser tree composed of: a root node Select-
Stm, a TargelList (projected attributes) and f o r each attribute contained in the clause Select a ResTarget
node that has a pointer to a node Attr , it contains the table name and a pointer to a Value node where is
indicated the name of the attribute. The SelectStmt node also has a fromClause list with a RangeVar node
for each input at the FROM clause, and a pointer to a node RelExpr with the table name, moreover the list
whereClause has a A_Expr node with the name of the operation, this is a subtree with two leaves: lexpr
(left term, in this case attribute “Age”) and rexpr (right term, in this case, A_FuzzyPred node “young”).

Fuzzy Query Tree

Next the parser module of PostgreSQLf transforms the fuzzy parser tree into a Fuzzy Query Tree. The
fuzzy condition is stored at the qualification structure , moreover the list of tables (or subquerys) are
stored at the rtable field as shown in Figure 5.