eclipse / ocl / org.eclipse.ocl / 3e1e6ffc64a93b4551ada2356f4b471df0920514 / . / examples / org.eclipse.ocl.examples.eventmanager / overview.html

A Registration represents an AndFilter with only elementary or negated | |

elementary filters. (In a future version, a Registration can represent | |

multiple equal such AndFilters.) | |

A Registration is entered into all tables for whose type its AndFilter | |

contains an elementary filter. | |

Each table maps a value for the filter criterion to a YesSet and a | |

NoSet. The YesSet contains all Registrations where a non-negated | |

elementary filter for the key criterion occurred. The NoSet contains | |

all Registrations where a negated elementary filter for the key | |

criterion occurred. | |

When an event occurs, it matches a Registration if and only if all | |

(negated and non-negated) elementary filters of the registration are | |

matched. This means that: | |

- if a Registration is in table t's YesSet, it MUST be matched by the | |

event e (R1). This in particular requires that e affects t. | |

- if a Registration is in a table t's NoSet, it MUST NOT be matched by | |

the event e (R2). This is in particular the case if e does not | |

affect t. | |

Formally, we can define a test function that for a given Registration | |

r and a given event e determines if the Registration if matched by the | |

event: | |

matches(r, e) := tables->forAll(t | | |

(t.allYes->includes(r) implies | |

(t.yes(e)->includes(r) and t.affectedBy(e))) | |

and (t.allNo->includes(r) implies | |

(not t.affectedBy(e) or not t.no(e)->includes(r)))) | |

Transformed: | |

matches(r, e) := tables->forAll(t | matches(t, r, e)) | |

matches(t, r, e) := | |

(not t.allYes->includes(r) or t.yes(e)->includes(r) and t.affectedBy(e)) | |

and (not t.allNo->includes(r) or not (t.no(e)->includes(r) and t.affectedBy(e))) | |

which shows that registrations neither in the allYes nor allNo of a | |

table t are matched by that table. | |

Thinking in sets, the set of registrations matching e is the | |

intersection of the sets of registrations matched by each table. The | |

problem with this definition is only that the "universe" of all | |

registrations to be considered is the union of all allYes and allNo | |

sets of all tables, computing which would be inefficient. | |

The challenge now is to compute all r for a given event e for which | |

matches(r, e) holds. Fast operations (O(1)) are t.allNo, t.allYes, | |

t.yes(e), t.no(e), also t.affectedBy(e). The number of Registrations r | |

may be large, and so may be t.allYes, t.allNo, t.yes(e) and t.no(e), | |

although typically t.allNo is fairly small, and so is t.no(e), | |

particularly in the context of the OCL impact analysis. | |

We also know that the union of t.allYes->union(t.allNo) over all | |

tables t results in the complete set of all Registrations. In other | |

words, each Registration to be considered is in the allYes or allNo | |

set of at least one table. The number of tables is constant and fairly | |

small (usually <10). | |

We are looking for a function | |

registrations(e) := all registrations r such that matches(r, e) | |

that can be computed efficiently. | |

TODO Special handling for multi-registrations, such as for multiple | |

classes in the class filter table: In this case the Registration is | |

matched if any of the multiple criteria are matched by the event. TODO | |

What happens for a negated filter that would expand to multiple | |

criteria? |