Submitted by Prerana Jainon May 28, Data Model A data model is a model that defines in which format the data are represented and accessed.
Next Page Databases are stored in file formats, which contain records. At physical level, the actual data is stored in electromagnetic format on some device. This storage is typically very small, ultra-fast, and volatile. Primary storage requires continuous power supply in order to maintain its state.
In case of a power failure, all its data is lost. Secondary storage includes memory devices that are not a part of the CPU chipset or motherboard, for example, magnetic disks, optical disks DVD, CD, etc. Since such storage devices are external to the computer system, they are the slowest in speed.
These storage devices are mostly used to take the back up of an entire system. Optical disks and magnetic tapes are widely used as tertiary storage. Memory Hierarchy A computer system has a well-defined hierarchy of memory. A CPU has direct access to it main memory as well as its inbuilt registers.
The access time of the main memory is obviously less than the CPU speed. To minimize this speed mismatch, cache memory is introduced. Cache memory provides the fastest access time and it contains data that is most frequently accessed by the CPU.
The memory with the fastest access is the costliest one. Larger storage devices offer slow speed and they are less expensive, however they can store huge volumes of data as compared to CPU registers or cache memory.
Magnetic Disks Hard disk drives are the most common secondary storage devices in present computer systems.
These are called magnetic disks because they use the concept of magnetization to store information. Hard disks consist of metal disks coated with magnetizable material.
These disks are placed vertically on a spindle. A magnetized spot can be recognized as 0 zero or 1 one. Hard disks are formatted in a well-defined order to store data efficiently.
A hard disk plate has many concentric circles on it, called tracks. Every track is further divided into sectors. A sector on a hard disk typically stores bytes of data. RAID consists of an array of disks in which multiple disks are connected together to achieve different goals.
RAID levels define the use of disk arrays. RAID 0 In this level, a striped array of disks is implemented. The data is broken down into blocks and the blocks are distributed among disks.
It enhances the speed and performance of the storage device. There is no parity and backup in Level 0.
When data is sent to a RAID controller, it sends a copy of data to all the disks in the array. Like level 0, each data bit in a word is recorded on a separate disk and ECC codes of the data words are stored on a different set disks.
Due to its complex structure and high cost, RAID 2 is not commercially available. The parity bit generated for data word is stored on a different disk. This technique makes it to overcome single disk failures. RAID 4 In this level, an entire block of data is written onto data disks and then the parity is generated and stored on a different disk.
Note that level 3 uses byte-level striping, whereas level 4 uses block-level striping.DBMS software itself, is the most important software component in the overall system; Operating system including network software being used in network, to share the data of database among multiple users.
Different Types of Database Users in DBMS: Four types of Database users in DBMS are Application Programmers, End Users, Casual, naive users DBA, System Analyst. Databases are stored in file formats, which contain records. At physical level, the actual data is stored in electromagnetic format on some device.
These storage devices can be broadly categorized into three types − A computer system has a well-defined hierarchy of memory.
A CPU has direct access. DBMS_XMLSCHEMA. DBMS_XMLSCHEMA package provides procedures to manage XML schemas. It is created by script grupobittia.com during Oracle database installation. Types dbms 1. DBMS 2. TYPES OF DATABASES Hierarchical database Network database Relational database Object-oriented database 3.
HIERARCHICAL DATABASE A DBMS is said to be hierarchical if the relationships among data in the database are established in such a way that one data item is present as the subordinate of another .
General: Note: DBMS_SQL is the traditional form of dynamic SQL in Oracle. For most purposes native dynamic sql (NDS) will suffice but there are some things the DBMS_SQL package does that can not be done any other way.