Question

Describe each questions:

Explain why the object-oriented database model was developed.

How does the OID in the OO model differ from the primary key in the relational model?

Is it possible for a superkey not to be a candidate key? Why or why not?

Briefly describe the four types of binary relationships possible between an entity set A and an entity set B based on relationship cardinality.

Sales Database:

Customer(custId, lastName, firstName, address, phone, creditLimit)

Order(orderNumber, date, total, custID)

LineItem(orderNumber, itemNumber, qtyOrdered).

Item(itemNumber, itemName, price)

For the Sales Database shown above, write the SQL command to find the item numbers of all items ordered by Sue Adams on June 10, 2015.

Explain why it is necessary to keep recovery logs in a database environment.

How do checkpoints help in recovery?

Why does a DBA create roles?

Explain the three components of the CIA model for information security.

Answer 1

Answer :

If you are writing an object oriented program where you objects are composed of several sub=objects and are linked together in your applications memory space you can spend a large percentage of you development of time writing the code to read, write and update you objects.

Many development shop use ORMs or Object Relational Mappers to reduce the effort required go from their internal object oriented structure to the external relational structure. This reduces the level of effort because typically ORMs have some intelligence and manage caching and dirty flags for you and can reduce the time to write all of the SQL calls manually.

A good OODBMS Object Oriented Database Management System can reduce this effort further still since the internal object structure of the program can match the external object structure of the database without having to go through the setup of the ORM translation layer.

But OODMSs do not have the same widely accepted standard for their query language and functionality that the major relational database based on the SQL standard do. In my opinion this is a major reason why their popularity is not much greater.

OODBMS’s can also have better performance characteristics in some application due to the fact that in many cases the data is pre-joined on disk and shares the same locality.

Answer 2:

The constraints supported by Object Oriented systems vary from system to system. The inverse relationship mechanism supported by some Object Oriented systems provides some declarative constraints.

the relational data base stores data in the form of tables which contains rows and columns. Every column in the table has its specific name and every row of the table has its own primary key. While in the object oriented database the data is stored in the form of objects. In the object oriented data the data is stored along with its actions that processes or reads the existing data.

Answer 3:

It is not necessary for a Super key to be always a candidate key because

• Super key is a set of one or more keys that can be used to identify a record uniquely in a table.Primary key, Unique key, Alternate key are subset of Super Keys.
• A Super Key is simply a non-minimal Candidate Key, that is to say one with additional columns not strictly required to ensure uniqueness of the row.
• A candidate key is a "minimal" super key - meaning the smallest subset of super key attributes which are unique. Removing any attribute from a candidate key would therefore make it non-unique.
• Candidate keys are those keys which is candidate for primary key of a table. In simple words we can understand that such type of keys which full fill all the requirements of primary key which is not null and have unique records is a candidate for primary key.

Answer 4:

Cardinality defines the number of entities in one entity set, which can be associated with the number of entities of other set via relationship set.

• One-to-one − One entity from entity set A can be associated with at most one entity of entity set B and vice versa.

• One-to-many − One entity from entity set A can be associated with more than one entities of entity set B however an entity from entity set B, can be associated with at most one entity.

• Many-to-one − More than one entities from entity set A can be associated with at most one entity of entity set B, however an entity from entity set B can be associated with more than one entity from entity set A.

• Many-to-many − One entity from A can be associated with more than one entity from B and vice versa.

Answer 5:Query :

select itemNumber from item where itemNumber in (
select itemNumber from LineItem where orderNumber in (
select OrderNumber from Order1 where custId in (
select custId from customer where firstName ='Sue' and lastName='Adams') and date1 ='10-6-15')
);

output:

Query 1 × f f貞0 |围 C 圈1 ▼| |すQL® Limit to 1000 rows 114 115 116 118 119 120 121 select itemNumber from item where itemNumber in ( select itemNumber from LineItem where orderNumber in ( select OrderNumber from Order1 where custId in ( Result Grid | 。 Filter Rows: Export: 1 Wrap Cell Content: A Result Grid item 2 × Read Only Output

Answer 6:

When more than one transaction are being executed in parallel, the logs are interleaved. At the time of recovery, it would become hard for the recovery system to backtrack all logs, and then start recovering. To ease this situation, most modern DBMS use the concept of 'checkpoints'.

Checkpoint

Keeping and maintaining logs in real time and in real environment may fill out all the memory space available in the system. As time passes, the log file may grow too big to be handled at all. Checkpoint is a mechanism where all the previous logs are removed from the system and stored permanently in a storage disk. Checkpoint declares a point before which the DBMS was in consistent state, and all the transactions were committed.

RECOVERY

• The recovery system reads the logs backwards from the end to the last checkpoint.

• It maintains two lists, an undo-list and a redo-list.

• If the recovery system sees a log with <T_n, Start> and <T_n, Commit> or just <T_n, Commit>, it puts the transaction in the redo-list.

• If the recovery system sees a log with <T_n, Start> but no commit or abort log found, it puts the transaction in undo-list.

All the transactions in the undo-list are then undone and their logs are removed. All the transactions in the redo-list and their previous logs are removed and then redone before saving their logs.

Answer 7:

Using roles has several benefits, including:

* Reducing the number of grants and thereby making it easier to manage security.

* Dynamically changing the privileges for many users with a single grant or revoke.

* Selectively enabling or disabling depending on the application.

Roles can be used for most system and object privileges. Privileges granted through a role cannot be used for creating an object (views, packages, procedures, and functions). You need to grant privileges directly to the user for this.

Answer 8:

here are three crucial components that make up the elements of the CIA triad, the widely-used model designed to guide IT security. Those components are confidentiality, integrity, and availability. Think of IT Security as you would a triangle…you need all three sides to make a whole.

Confidentiality is the set of rules which limits access to information. It is important to protect confidentiality by restricting access to those who are authorized to view that data. This is one reason data and system classification is so important. Some risks associated with lack of confidentiality are loss of privacy, unauthorized access to information, and identity theft.

Integrity is the assurance that the information is trustworthy and accurate. Data must not change in transit and must be protected from alteration by unauthorized parties. User access controls must be in place and backups must be available for restoring affected data. Some risks involved with not protecting the integrity of data are fraud and information that is no longer reliable or accurate.

Availability is the guarantee that information can be accessed by authorized personnel. Availability is ensured by maintaining hardware and software, as well as having data backups and a good disaster recovery plan for the worst case scenario. Risks associated with lack of availability are business disruption, loss of revenue, and loss of reputation.

As you can see, the three core components of IT Security are critical for protecting the Institute’s data. No one component is more important than the others, as they are all three equally vital to IT security.