This essay focuses on clean mathematical definitions. The source’s validity and usefulness for your research topic. Write at least 5 sentences per annotation.
1. Find 3 appropriate scholarly PEER-REVIEWED resources concerning the topic. All these sources must come from EFSC on-line databases, To access theses sources, you have to log into MY EFSC, – Library Resources – DATABASES. Remember that you WILL NOT GET ANY CREDIT for any open-access sources obtain through a GOOGLE search (or any other search engine). 2.
Not just as publications in print or posts on the web (see an MLA directory in a textbook of your choice or use Purdue OWL). 4. Create an MLA-style annotation to each source. Every annotation must include a brief summary of the source and a brief explanation. The source’s validity and usefulness for your research topic. Write at least 5 sentences per annotation.
The use of primary keys (user-orient identifiers) to represent cross-table relationships. Rather than disk addresses, had two primary motivations. From an engineering perspective, it enable tables to be relocate and resize without expensive database reorganization. But Codd was more interest in the difference in semantics. The use of explicit identifiers made it easier to define update operations with clean mathematical definitions.
Because these operations have clean mathematical properties, it becomes possible to rewrite queries in provably correct ways. Which is the basis of query optimization. There is no loss of expressiveness compare with the hierarchic or network models. Though the connections between tables are no longer so explicit.
In the hierarchic and network models, records were allow to have a complex internal structure. For example, the salary history of an employee might be represent as a “repeating group” within the employee record. In the relational model, the process of normalization laed to such internal structures being replace by data hold in multiple tables. Connect only by logical keys.
Their name, login information, various addresses and phone numbers. In the navigational approach, all of this data would be placed in a single variable-length record. In the relational approach, the data would be into a user table, an address table and a phone number table (for instance). Records would be create in these optional tables only if the address or phone numbers were actually provide.