The Schema::createRel() function is used to create a relation. Creating a relation involves adding the relevant records to the relation catalog and the attribute catalog (using BlockAccess::insert()). Before this can be done, the user input will need to be verified to ensure that there are no existing relations with the same name. Additionally, it will also need to be verified that the new relation does not contain duplicate attribute names.
Question
The Schema::createRel() function is used to create a relation. Creating a relation involves adding the relevant records to the relation catalog and the attribute catalog (using BlockAccess::insert()). Before this can be done, the user input will need to be verified to ensure that there are no existing relations with the same name. Additionally, it will also need to be verified that the new relation does not contain duplicate attribute names.
Solution 1
La funzione Schema::createRel() viene utilizzata per creare una relazione. Creare una relazione implica l'aggiunta dei record pertinenti al catalogo delle relazioni e al catalogo degli attributi (utilizzando BlockAccess::insert()). Prima che ciò possa essere fatto, sarà necessario verificare l'input dell'utente per assicurarsi che non esistano relazioni con lo stesso nome. Inoltre, sarà anche necessario verificare che la nuova relazione non contenga nomi di attributi duplicati.
Solution 2
La funzione Schema::createRel() viene utilizzata per creare una relazione. Creare una relazione implica l'aggiunta dei record pertinenti al catalogo delle relazioni e al catalogo degli attributi (utilizzando BlockAccess::insert()). Prima che ciò possa essere fatto, sarà necessario verificare l'input dell'utente per assicurarsi che non esistano relazioni con lo stesso nome. Inoltre, sarà anche necessario verificare che la nuova relazione non contenga nomi di attributi duplicati.
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int Schema::deleteRel(char *relName) { // if the relation to delete is either Relation Catalog or Attribute Catalog, // return E_NOTPERMITTED // (check if the relation names are either "RELATIONCAT" and "ATTRIBUTECAT". // you may use the following constants: RELCAT_NAME and ATTRCAT_NAME) // get the rel-id using appropriate method of OpenRelTable class by // passing relation name as argument // if relation is opened in open relation table, return E_RELOPEN // Call BlockAccess::deleteRelation() with appropriate argument. // return the value returned by the above deleteRelation() call /* the only that should be returned from deleteRelation() is E_RELNOTEXIST. The deleteRelation call may return E_OUTOFBOUND from the call to loadBlockAndGetBufferPtr, but if your implementation so far has been correct, it should not reach that point. That error could only occur if the BlockBuffer was initialized with an invalid block number. */}
For each attribute of a relation, there is a set of permitted values, called the ________ of that attribute.DomainSetRelationSchema
Properties of RelationalDecompositions (2) Relation Decomposition andInsufficiency of Normal Forms (cont.): Decomposition: The process of decomposing the universal relationschema R into a set of relation schemas D ={R1,R2, …, Rm} that will become the relationaldatabase schema by using the functionaldependencies. Attribute preservation condition: Each attribute in R will appear in at least onerelation schema Ri in the decomposition so that noattributes are “lost”.
how to create a new schema and then the new model
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