Web design course - Primary key A key uniquely identifying each row in
Primary key A key uniquely identifying each row in a table. The entity on the many side of the relationship has a foreign key. The foreign key column contains primary key values of the entity on the one side of the relationship. Projection Normal Form (PJNF) See 5th Normal Form. Query A statement interrogating the database and returning information. Most often tables are interrogated and records from those tables are returned. Queries can be both simple and complex. A query is executed using the SQL SELECT command. Random access memory (RAM) The memory chips inside your computer. RAM provides an ultrafast buffering storage area between CPU (the processor) and your I/O devices (disks). RDBMS See Relational Database Management System. Record A repetition of a field structure across a table. Records repeat field structure in a table, where each repeated field can (and sometimes should) have a different value. Tables are divided into fields and records. Fields impose structure and datatype specifics onto each of the field values, in each record. Redundant Array of Inexpensive Disks (RAID) A bunch of small, cheap disks. A RAID array is a group of disks used together as a single unit logical disk. RAID arrays can help with storage capacity, recoverability and performance, using what are called mirroring and striping. Mirroring creates duplicate copies of all physical data. Striping breaks data into many small pieces, where those small pieces can be accessed in parallel. Referential integrity A process (usually contained within a relational database model) of validation between related primary and foreign key field values. For example, a foreign key value cannot be added to a table unless the related primary key value exists in the parent table. Similarly, deleting a primary key value necessitates removing all records in subsidiary tables, containing that primary key value in foreign key fields. Additionally, it follows that preventing the deletion of a primary key record is not allowed if a foreign key exists elsewhere. Relational Database Management System (RDBMS) A system that uses a database that contains tables with data. The management system part is the part allowing you access to that database, and the power to manipulate both the database and the data contained within it. Relational database model A model that provides a two-dimensional structure to data. The relational database model more or less throws out the window the concept and restriction of a hierarchical structure, but does not completely abandon data hierarchies. Any table can be accessed directly with having to access all parent objects. Precise data values (such as primary keys) are required to facilitate skirting the hierarchy (to find individual records) in specific tables. Replication A method used to duplicate (replicate) and distribute data from a primary or master database, out to a number of other copies of the master database. Those copies can be fully dependent slave databases, or even other master databases, capable of passing their own changes back. Right outer join A query finding the combination of intersection, plus records in the right-sided table, but not in the left-sided table. 416 Glossary
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