The database security is broadly classified into physical and logical security. Database recovery is the way of restoring a database to a correct state in the event of a failure.Physical security − Physical security refers to the security of the hardware that is associated with the system and the protection of the site where the computer resides. The natural events like fire, floods, and earthquakes can be considered as some of the physical threats. It is advisable to have backup copies of databases in the face of massive disasters.Logical security − Logical security refers to the security measures present in ... Read More

Query Processing is a translation of high-level queries into low-level expression. It is a step wise process that can be used at the physical level of the file system, query optimization and actual execution of the query to get the result.It requires the basic concepts of relational algebra and file structure. It refers to the range of activities that are involved in extracting data from the database. It includes translation of queries in high-level database languages into expressions that can be implemented at the physical level of the file system.Given below is the diagram that shows the steps of the ... Read More

In parallel database system data processing performance is improved by using multiple resources in parallel. In this CPU, the disk is used parallel to enhance the processing performance.Operations like data loading and query processing are performed parallel. The centralized and client server database systems are not powerful enough to handle applications which need fast processing.Parallel database systems have great advantages for online transaction processing and decision support applications. Parallel processing divides a large task into multiple tasks and each task is performed concurrently on several nodes. This gives a larger task to complete more quickly.Architectural ModelsThere are several architectural models ... Read More

Logical Database Design has a low-level description of entities that are defined and how they are related to each other and what kind of data is to be stored. This model determines if all the requirements of the business have been gathered.Physical Database Design deals with how the data will be stored in the database using suitable DBMS and this design is generally created by database administrators and developers.DifferencesThe major differences between logical database design and physical database design are as follows −Logical Database DesignPhysical Database DesignThat describes the data without regard to how they will be physically implemented in ... Read More

Physical database designing is used for good performance while the process of structuring data in the storage.Factors influencing physical database designLet us see the important factors that influence physical database design −Transactions and queriesIt is important to understand what kind of transactions and queries will be run and what use will the database serve.Following information about the queries should be needed −Files that will query access.Selection conditions to be specified for the query.Type of selection conditions to be used in query whether equality, range, or inequality.Join conditions to be used in the query.Need for linking tables for query optimization.Following information ... Read More

For any stored data if we want to preserve the consistency and correctness, a relational DBMS typically imposes one or more data integrity constraints. These constraints restrict the data values which can be inserted into the database or created by a database update.Data Integrity ConstraintsThere are different types of data integrity constraints that are commonly found in relational databases, including the following −Required data − Some columns in a database contain a valid data value in each row; they are not allowed to contain NULL values. In the sample database, every order has an associated customer who placed the order. ... Read More

ProblemCreate a B-Tree of order 4 for the following set of key values −1, 12, 8, 2, 25, 6, 14, 28, 17, 7, 52, 16, 48, 68, 3SolutionLet us start constructing B-Tree step by step −Step 1 − As the given order is 4, the first four items go into root and are arranged in sorted order (ascending). Step 2 − Now, we need to insert the fifth element, if we insert the fifth item in root it violates the condition, because the order is 4. Step 3 − So, when 25 arrives pick ... Read More

Let us first try to understand why we are using B-tree. Then, we will get a clarity on the definition of B-tree.Reasons for using B-treeThe reasons for using B-tree are as follows −When searching tables on disc, the cost of accessing the disk is high but it doesn’t bother about the amount of data transferred. So our aim is to minimize disc access.We know that we cannot improve the height of trees. So, we wish to make the height of the tree as small as possible.The solution for this is to use a B-tree, it has more branches and thus ... Read More

The advantages and disadvantages of some of the collision resolution techniques are explained below −Separate Chaining hashingSeparate chaining is a hashing technique in which there is a list to handle collisions. So there are many elements at the same position and they are in a list. The sequences are maintained in a linked list.The advantages of separate chaining hashing are as follows −Separate chaining technique is not sensitive to the size of the table.The idea and the implementation are simple.The disadvantages of separate chaining hashing are as follows −Keys are not evenly distributed in separate chaining.Separate chaining can lead to ... Read More

Collision is a problem that occurs when two keys applied on a hash table map to the same location in the hash table.There are two techniques that are used to avoid collision they are −Linear probing.Chaining.Let us discuss each technique in detail.Linear probingLinear probing is a strategy for resolving collisions. In this the new key is placed in the closest following empty cell.Here the elements are stored wherever the hash function maps into a hash table, if that cell is filled then the next consecutive location is searched to store that value. Here generally we use arrays.Step 1 − Let ... Read More