62. Data independence meansA. data is defined separately and not included in programs.B. programs are not dependent on the physical attributes of dataC. programs are not dependent on the logical attributes of dataD. both B and CAnswer: D
63. A.........is used to define overall design of the database
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64. Key to represent relationship between tables is called
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65. Grant and revoke are.......statements.
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Green- EasyRed- IntermediateBlack- Challenging66. DBMS helps achieveA. Data independenceB. Centralized control of dataC. Neither A nor BD. Both A and BAnswer: D
67...........command can be used to modify a column in a table
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68. The ascending order of a data hirerchy is:
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69. Which of the following is true of a network structure?
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70. Which of the following is a problem of file management system?A.difficult to updateB.lack of data independenceC.data redundancyD.program dependence
Green- EasyRed- IntermediateBlack- ChallengingE.all of aboveAnswer: E71. One data dictionery software package is called
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72. The function of a database is ...
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73. What is the language used by most of the DBMSs for helping their users to access data?
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74. The model for a record management system might beA.handwritten listB.a Rolodex card fileC.a business formD.all of aboveAnswer: D
75. Primitive operations common to all record management system include
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Green- EasyRed- IntermediateBlack- Challenging
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If a database system is not multi-layered, then it becomes difficult to make any changes in the database system. Database systems are designed in multi-layers as we learnt earlier.
Data Independence
A database system normally contains a lot of data in addition to users’ data. For example, it stores data about data, known as metadata, to locate and retrieve data easily. It is rather difficult to modify or update a set of metadata once it is stored in the database. But as a DBMS expands, it needs to change over time to satisfy the requirements of the users. If the entire data is dependent, it would become a tedious and highly complex job.
Metadata itself follows a layered architecture, so that when we change data at one layer, it does not affect the data at another level. This data is independent but mapped to each other.
Logical Data Independence
Logical data is data about database, that is, it stores information about how data is managed inside. For example, a table [relation] stored in the database and all its constraints, applied on that relation.
Logical data independence is a kind of mechanism, which liberalizes itself from actual data stored on the disk. If we do some changes on table format, it should not change the data residing on the disk.
Physical Data Independence
All the schemas are logical, and the actual data is stored in bit format on the disk. Physical data independence is the power to change the physical data without impacting the schema or logical data.
For example, in case we want to change or upgrade the storage system itself − suppose we want to replace hard-disks with SSD − it should not have any impact on the logical data or schemas.