database-normalization

问题 I started to teach myself the basics of databases and i am currently working through 1. to 3. normal forms. What i understand until now is the wish to remove redundancy to make my databases less prone to inconsistency during phases of data-change as well as saving space by eliminating as much duplicates as possible. For example if we have a table with the following columns: CD_ID title artist year and change the design to have multiple tables where the first (CD) contains: CD_ID title artist

问题 From the "A Simple Guide to Five Normal Forms in Relational Database Theory": Fourth and fifth normal forms both deal with combinations of multivalued facts. One difference is that the facts dealt with under fifth normal form are not independent, in the sense discussed earlier. Following rule has been mentioned: Suppose that a certain rule was in effect: if an agent sells a certain product, and he represents a company making that product, then he sells that product for that company. ACP -----

问题 From the "A Simple Guide to Five Normal Forms in Relational Database Theory": Fourth and fifth normal forms both deal with combinations of multivalued facts. One difference is that the facts dealt with under fifth normal form are not independent, in the sense discussed earlier. Following rule has been mentioned: Suppose that a certain rule was in effect: if an agent sells a certain product, and he represents a company making that product, then he sells that product for that company. ACP -----

问题 From the "A Simple Guide to Five Normal Forms in Relational Database Theory": Fourth and fifth normal forms both deal with combinations of multivalued facts. One difference is that the facts dealt with under fifth normal form are not independent, in the sense discussed earlier. Following rule has been mentioned: Suppose that a certain rule was in effect: if an agent sells a certain product, and he represents a company making that product, then he sells that product for that company. ACP -----

问题 When can a BCNF decomposition not preserve functional dependency... I am trying to figure this out for say R=(V,W,X,Y,Z) 回答1: The point of a BCNF decomposition is to eliminate functional dependencies that are not of the form key -> everything else So if a table has a FD, say A -> B, such that A is not a key, it means you're storing redundant data in your table. As a result, you create a new table with columns A and B, with A being the key, then you remove B from your original table. As a

问题 Suppose we have the following table structures: Humans | HumanID | FirstName | LastName | Gender | |---------+-----------+----------+--------| | 1 | Issac | Newton | M | | 2 | Marie | Curie | F | | 3 | Tim | Duncan | M | Animals | AmimalID | Species | NickName | |----------+---------+----------| | 4 | Tiger | Ronnie | | 5 | Dog | Snoopy | | 6 | Dog | Bear | | 7 | Cat | Sleepy | I wonder how to reference a group of records in other tables. For example, I have a Foods table and an EatenBy

问题 Whenever a proper ER diagram is drawn for a database and then mapped to the relational schema, I was informed that it guarantees 3NF . Is this claim true? If not, can anyone provide me a counter example. Also, please tell me whether any normal form can be claimed to be strictly followed when relational schema is mapped from a perfect ER diagram? 回答1: The short answer is no. Depending on the analysis and design approach there could be examples of ER models that appear perfectly sound in ER

问题 I have a product table that contains two column ProductID Desc 1 Fan 2 Table 3 Bulb I have another table that contains supplier information SupplierID Desc 1 ABC 2 XYZ 3 HJK Now One supplier can supply multiple products and one product can be supplied by multiple suppliers To achieve this I have created another table tbl_Supplier_Product SupplierID ProductID 1 1 1 2 2 1 2 2 2 3 Is it a good way to link this table to supplier and product table through primary composite key. In this table the

问题 I am designing a System which has different types of Addresses. For example, a Person Address, A Hotel Address, An Airport Address, An Office Address. I am involved in a discussion where I am of the opinion that as the addresses are different(of different entities Hotel, Airport etc.) the addresses should be stored in separate tables. I think this would improve performance. There is another opinion to have all the addresses in the same table. I am using PostgreSQL and am looking at over 10

问题 I am working through an example problem in which we are trying to identify which of the following relations is in Third Normal Form (3NF). Here are the relations we are given: R1(ABCD) ACD -> B   AC -> D   D -> C   AC -> B R2(ABCD) AB -> C   ABD -> C   ABC -> D   AC -> D R3(ABCD) C -> B   A -> B   CD -> A   BCD -> A R4(ABCD) C -> B   B -> A   AC -> D   AC -> B I know the answer is R1 is in 3NF, but I'm having a hard time understanding the steps to go about determining what violates 3NF. Can