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2 customers have more than one phone number. That is the same as "at least one customer has more than one phone number". Therefore, to record the correct customer information you must allow for more than one phone number. If you provide Phone1 and Phone2 fields for two phone numbers you meet the requirement, however you have wasted space for a second phone on all but two customers. If you had provided a second child table for phone numbers you would have all but two customers with one record and the two others would have two records (no wasted space).
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What are the main differences between relational algebra and relational calculus?
Relation algebra is a procedural language where relation calculus is non-procedural languageRelational algebra, an offshoot of first-orderlogic (and of algebra of sets), deals with a set of finitaryrelations (see also relation (database)) which is closed under certain operators. These operators operate on one or more relations to yield a relation. Relational algebra is a part of computer science.Relational calculus consists of two calculi, the tuplerelational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries. This in contrast to the relational algebra which is also part of the relational model but provides a more procedural way for specifying queries.The relational algebra might suggest these steps to retrieve the phone numbers and names of book stores that supply Some Sample Book:1. Join books and titles over the BookstoreID.2. Restrict the result of that join to tuplesfor the book Some Sample Book.3. Project the result of that restriction over StoreNameand StorePhone.The relational calculus would formulate a descriptive, declarative way:Get StoreNameand StorePhonefor supplies such that there exists a title BK with the same BookstoreIDvalue and with a BookTitlevalue of Some Sample Book.The relational algebra and the relational calculus are essentially logically equivalent: for any algebraic expression, there is an equivalent expression in the calculus, and vice versa.This result is known as Codd'stheorem
What is domain in calculus?
In calculus, the domain refers to the interval that all x values fall on in a graph, equation, etc.
Describe the differences in meaning between the terms relation and relation schema?
Relational Schema refers to meta-data elements which are used to describe structures and constraints of data representing a particular domain. Whereas a relation is a property or predicate that ranges over more than one argument Here's some translation from "Relational Algebra" to SQL terminology: * "Relation" = Table. * "Relation Schema" = Table definition. So for example, the "schema" for the Person "relation" is: Person(FirstName, LastName, Age, Gender, Address) Also in relational Algebra, a "tuple" is a table row, and an "attribute" is a table column.Mathematician define a relation to be subset of cartesian product list of domains.In daabase relation is a set of entities with similar attributes.In other way we can consider a relation as a table and it's rows as entities, and table's columns as attributes.Concept of relation corresponds to programming language notion of variable.relational Schema corresponds to the programming language notion of type definition.It is the logical design of database.e.g. for a relation account having attributes account_number, branch_name and balance, relational schema is specified as -Account_schema= (account_number, branch_name, balance)
Which relation are function relation?
A relation is a mapping between two sets, a domain and a range. A function is a relationship which allocates, to each element of the domain, exactly one element of the range although several elements of the domain may be mapped to the same element in the range.
What is domein in algebra?
The domain is all the first coordinates in a relation. A relation is two ordered pairs.
