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CS Notes for Lecture
CORAL
Develop ed by Raghu Ramakrishnan at Wisconsin Similar in many resp ects to NAILGLUE but
All mo dules are declarative no GLUEstyle control ow
Programmer can declare the approach to b e used to evaluate the predicates of a mo dule Strategies include
a Seminaive magicsets
b Seminaive tailrecursion elimination as in Ch of PDKSI I
c Topdown using Prologlike algorithm
Built on top of Exo dus data manager Sup p orts transactions but like NAIL it is really a mainmemory system
Store tuples with variables Allows facts like ancX X everyone is hisher own ances tor Also gives a magicsets algorithm that avoids the need for subgoal rectication see Sect of PDKSI I
C interface
C extended with classes for relations
Subgoals in CORAL can b e C pro ce dures
Negation in CORAL
Supp orts mo dularly stratied negation and takes advantage of magicsets
Trick work on lowest mo dule p ossible at all times
A rule for a magic predicate b elongs to the mo dule of the rule that spawned the magic rule by the Group I construction
Ab ove rule OK even though there may b e intermo dule recursions that result b ecause we will judiciously order the ring of rules
Example Here are nonrecursive rules that b e come recursive when magicsets is applied
qXY qXZ pZY pXY aXY
Query q bf^
If we use simplied magicsets and skip the supplementary predicate we get m pZ m qX qXZ qXY m qX qXZ pZY pXY m pX aXY
There is a recursive cycle
m p p q m p
Handling Negation Magic Sets
Simple example just plain stratied
onlyXY arcXY not path XY path XY arcXZ arcZY
onl y X Y means there is an arc from no de X to Y but no path of length from X to Y
Stratum far c pathg Stratum fonl y g
Query onl y f^ f^
Note m onl y has arguments in eect the initializer is m only true We can just drop m onl y instead r m path XY arcXY r path XY m path XY arcXZ arcZY r onlyXY m path XY not path XY
Supp ose EDB f g
Tuples have ob jectIDs
One can reference tuples by a reference variable eg p Name for the Name comp onent of the tuple referenced by p
There is a conventional OO typ e system in cluding typ es that are lists sets bags or ar rays of other typ es
There is inheritance by sub classes
Classes can have metho ds
Atoms are written with their arguments as attribute value
Example
eponame sally phone P office O
An argument whose value is a variable ap p earing only once in a rule need not app ear
Language Structure
Similar to GLUENAIL an imp erative com p onent and a declarative comp onent
Declarative rules lo ok like Datalog but with the style of atoms indicated ab ove instead of and logical connectives as words eg AND
Example
pathfirst X last Y arctail X head Z AND arctail Z head Y
Imp erative statements include insert delete if switch create for classespredicates new for creating new ob jects and the foreach iterator construct illustrated b elow
Example Supp ose we have a class emp with at tributes that include salary of typ e integer and mgr of typ e refemp ie a reference to an em ployee ob ject
The following deletes all employees who make more than their managers FOREACH erefemp IN SET OF X FROM XempsalaryS mgrm DO IFS m salary DELETE e
Line declares X to range over the emp ob jects that have a salary and manager attribute if there are sub classes p erhaps some do not It also gives names S to the salary and m to the reference to the manager
Line declares e to b e a p ointer refer ence ranging over all the tuples in the set constructed in line
Line tests whether the salary of the em ployee is greater than the salary of the man ager employee p ointed to by m and deletes the employee ob ject if so
