9/28/2023 0 Comments Dbms basic concepts![]() DB2 ensures that only valid data is allowed within DB2. If an integrity constraint states that no salaries can exceed $100,000, then any transaction violating this rule will be aborted. This means that a transaction can’t break the rules, or integrity constraints, of the database. Refers to the database being in a legal state when the transaction begins and when it ends. A transfer of funds can be completed or it can fail for a multitude of reasons, but atomicity guarantees that one account won’t be debited if the other is not credited as well. Refers to the ability of the DBMS to guarantee that either all of the tasks of a transaction are performed or none of them are. From examples during this course, you will see that DB2 does apply the characteristics of this model: Data integrity – Database theory demands that all changes to data follow the ACID model.Recovery – Restoring DB2 data due to outages, system failures or corruption by incorrect program logic.Locking – Serializing the access to DB2 data in order to allow concurrency, while guaranteeing data integrity.Optimization – Minimizing the use of system resources (CPU cycles and physical I/O) when performing SQL queries and doing other DB2 work.Security – Monitoring and controlling access to DB2 data.Logging – Saving “before” and “after” images (called UNDO and REDO records) of any DB2 rows changed by SQL (INSERT, UPDATE, DELETE).Load data into a DBMSĭatabase managers provide many services, such as: At each juncture of a row and column, one and only one value may be present, according to relational theory. The rows in a relational database may or may not be in a particular order.Ī relational database is a table database, consisting of rows and columns. Phone books are in alphabetical sequence. Each page has the same columns (name, address, and phone number), just different rows. A phone book is another example of a table of data. An Excel spreadsheet usually consists of rows and columns. The ease of working with a relational database We will discuss potential tasks associated with DB2, and the various I/T roles that support and use the DB2 environment. ![]() In this unit we will discuss the basic structure of a table, and will mention three characteristics that are assigned to all columns. End users and applications access DB2 data through SQL. Relational database managers understand SQL, the programming language for relational databases. A relational database is one in which the data is perceived as being stored in rows and columns. The word relation is simply a synonym for the word table. We will discuss some of the more commonly used DB2 services in this course. ![]() Each database manager provides a set of automated services. Define the roles that are performed within DB2ĭatabase managers are sophisticated software programs that maintain our data.Define the tasks performed by DB2 when running an application. ![]()
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