RDBMS - Advance 2

51. What is the difference between SQL Server 2000 complete and differential backups?

Ans: A complete backup makes a copy of the entire database. A differential backup makes a copy of the changes that have been made to the database since the last complete backup. A complete backup must be made before the first differential backup. Because differential backups are faster, they can be taken more frequently and the chance of data loss is reduced. Complete backups take longer but are slightly simpler to use for recovery.

52. Explain the meaning of each of the transaction levels supported by SQL Server.

Ans: The strictest isolation level is SERIALIZABLE. With it, SQL Server places a range lock on the rows that have been read. This level is the most expensive to use and should only be used when absolutely required. The next most restrictive level is REPEATABLE READ, which means SQL Server places and holds locks on all rows that are read. It is possible to make dirty reads by setting the isolation level to READ UNCOMMITTED, which is the least restrictive level. READ COMMITTED is the default isolation level.

53. Explain the difference between the SQL Server 2000 simple, full, and bulk-logged recovery models.

Ans: With the simple recovery model, no logging is done. The only way to recover a database is to restore the database to the last backup. With full recovery, all database changes are logged. With bulk-logged database recovery, all changes are logged except those that cause large log entries.

54. What is the difference between SQL Server 2000 clustered and nonclustered indexes?

Ans: With a clustered index, the data are stored in the bottom level of the index and in the same order as that index. With a nonclustered index, the bottom level of an index does not contain data; it contains pointers to the data. For data retrieval, clustered indexes are faster than nonclustered indexes.

55. What triggers does SQL Server 2000 support?

Ans: SQL Server 2000 supports INSTEAD OF and AFTER triggers only. There is no SQL Server support for BEFORE triggers. A table may have one or more AFTER triggers for insert, update and delete actions; AFTER triggers may not be assigned to views. A view or table may have at most one INSTEAD OF trigger for each triggering action of insert, update or delete.

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56. What is the relationship of ODBC, OLE DB, and ADO?

Developed first, the ODBC standard is for relational databases; while the OLE DB standard provides functionality for both relational and other databases. Finally, ADO was developed to provide easier access to OLE DB data for the non-object-oriented programmer.

57. What are the three types of data sources used with ODBC?

Ans: An ODBC file data source is a file that can be shared among database users. A ODBC system data source is one that is local to a single computer. A ODBC user data source is only available to the user who created it.

58. What disadvantage of ODBC does OLE DB overcome?

Ans: By breaking the features and the functions of a DBMS into COM objects, OLE DB characteristic overcomes a major disadvantage of ODBC. With ODBC, a vendor must create an ODBC driver for almost all DBMS features and functions in order to participate in ODBC at all. This is a large task that requires a substantial initial investment. With OLE DB, however, a DBMS vendor can implement portions of their product.

59. What are to goals of OLE DB?

Ans: The major goals of OLE DB are to: (1) Create object interfaces for DBMS functionality pieces; (2) Increase flexibility for developers and users; (3) provide an object interface over any type of data; and (4) do not force data to be converted or moved from where it is.

60. In OLE DB, what is the difference between an interface and an implementation?

Ans: An OLE DB interface is specified by a set of objects, and the properties and methods that they expose, and OLE DB defines standardized interfaces. An object need not expose all of its properties and methods in a given interface. An OLE DB implementation defines how the object supports the interface. The implementation is completely hidden from the user. Thus developers of an object are free to change the implementation whenever they want, but they should not change the interface without consulting their users.

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61. Why is XML a better markup language than HTML?

Ans: XML is a better markup language than HTML, primarily because XML provides a clear separation between document structure, content, and materialization. Symbols cannot be used ambiguously with XML.

62. What are the two means to describe the content of XML documents?

Ans: DTD (Document Type Declarations) and XML Schemas. An XML document that conforms to its DTD is called type-valid. A document can be well-formed and not be type-valid, either because it violates the structure of its DTD or because it has no DTD. However, DTDs have limitations and to overcome these limits XML Schemas were created. XML Schemas are XML documents that are the preferred method for defining document structure.

63. What is the difference between simple elements and complexType elements?

Ans: Simple elements have only one data value. ComplexType elements can have multiple elements nested within them. ComplexTypes may also have attributes. The elements contained in a complexType may be simple or other complexTypes. ComplexTypes may also define element sequences.

64. What is ADO.NET?

Ans: ADO.NET is a new, improved, and greatly expanded version of ADO that was developed for the Microsoft .NET initiative. ADO.NET incorporates all of the functionality of ADO, but adds much more. In particular, ADO.NET facilitates the transformation of XML documents to and from database data. Most importantly, ADO.NET introduces the concept of datasets, which are in-memory, full-function, independent databases.

65. What is a dataset?

Ans: A dataset is an in-memory database that is disconnected from any regular database, but has all the important characteristics of a regular database. Datasets can have multiple tables, relationships, referential integrity rules, referential integrity actions, views and the equivalent of triggers. Datasets are needed to provide a standardized, non-proprietary means to process database views. They are especially important for the processing of views with multiple multivalued paths.

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66. Briefly describe the four JDBC driver types that Sun defines.

Ans: Type 1 drivers provide a bridge between Java and ODBC. Types 2-4 drivers are written entirely in Java, but differ as to how they connect to the DBMS. Type 2 drivers rely on the DBMS product for intermachine communication, if any. Type 3 drivers translate JDBC calls into a DBMS-independent network protocol. Type 4 drivers translate JDBC calls into a DBMS-dependent network protocol.

67. What is the difference between a Java servlet and a Java applet?

Ans: An applet is a compiled Java bytecode program that is transmitted to a browser via HTTP and is invoked using the HTTP protocol on the user's workstation. A servlet is a Java program that is invoked on the server to respond to HTTP requests.

68. What is the coding pattern for using a JDBC driver?

Ans:

1. Load the driver.

2. Establish a connection to the database.

3. Create a statement.

4. Do something with the statement.

69. What is a Java bean?

Ans: A Java bean is a Java class that has the following three properties.

(1) There are no public instance variables.

(2) All persistent values are accessed using methods named getxxx and setxxx.

(3) The bean class must either have no constructors or it must have one explicitly defined zero-argument constructor.

70. How are surrogate keys and metadata handled in MySQL?

Ans: MySQL uses integer data types combined with the property AUTO_INCREMENT to create surrogate keys. This creates a sequence that starts at one (1) and increases by one (1) for each new record. MySql maintain its metadata in a database named mysql. For example, this database maintains two tables named user and db.

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71. What is a data mart?

Ans: A data mart is a collection of data smaller in scope and size than a data warehouse. It is dedicated to data from a particular business component of business functional area. A data mart may function as a subset of a larger data warehouse. Users of a data mart are usually knowledgeable analysts in the business area using the data mart.

72. What is RFM analysis?

Ans: RFM analysis is a Business Intelligence (BI) reporting system that analyzes and ranks customers based on their purchasing patterns. R refers to "how recently" a customer placed an order, F refers to "how frequently" the customer orders, and M refers to "how much money" the customer spends. Typically, the customers are ranked into "20%" groups and assigned a number to represent their ranking. Thus 1 means top 20%, 2 the next 20% and so on. In this system a score of 1 is best and a score of 5 is worst. Thus a customer with an RFM score = 1 5 1 would be one who has ordered recently, does not order frequently, and who makes large purchases.

73. What are the functions of a reporting system?

Ans: A reporting system has three functions: 1. Report authoring -- connecting to data sources, creating the report structure and formatting the report. 2. Report management -- defining who receives which reports, when they receive them and how the reports are delivered. 3. Report delivery -- based on report management metadata, either pushing the reports to the recipients or allowing them to be pulled by the recipients.

74. What is OLAP?

Ans: OnLine Analytical Processing (OLAP) is a Business Intelligence (BI) reporting system. OLAP provides the user with the capability to sum, count, average and do other simple arithmetic operations on groups of data. An OLAP report has measures and dimensions. Measures are the data values to be displayed. Dimensions are characteristics of the measures. OLAP reports are called OLAP cubes, although such reports are not limited to three dimensions.

75. What is market basket analysis?

Ans: Market basket analysis is a data mining technique that determines which sets of products tend to be purchased together. A common technique uses conditional probabilities. In addition to the basic probability that an item will be purchased, three results are of particular interest:

Support -- the probability of two items being purchased together.

Confidence -- the probability of a second item being purchased GIVEN that another item has been purchased.

Lift -- calculated as confidence divided by a basic probability, this shows the likelihood of a second item being purchased IF an item is purchased.

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76. Explain the differences between structured data and unstructured data.

Ans: Structured data are facts concerning objects and events. The most important structured data are numeric, character, and dates. Structured data are stored in tabular form. Unstructured data are multimedia data such as documents, photographs, maps, images, sound, and video clips. Unstructured data are most commonly found on Web servers and Web-enabled databases.

77. Explain why it is still necessary to have at least some familiarity with file processing systems even though it has become evident that traditional file processing systems have a number of shortcomings and limitations.

Ans: Many businesses still use file processing systems today. This is especially true in the creation of backups for a database system. In addition, if you understand some of the limitations of a file processing system such as program-data dependence, duplication of data, limited data sharing, lengthy development times, and excessive program maintenance, you can try and avoid them as you design and develop a databases.

78. What are some of the disadvantages associated with conventional file processing systems?

Ans: There are five disadvantages. Program-data dependence occurs when file descriptions need to be changed in all programs whenever a file description changes. Duplication of data is storing the data more than one time. Limited data sharing occurs when the files are private so no one outside of one application can access the data. Lengthy development times exist because file processing systems takes longer to develop. Lastly, excessive program maintenance exists since the effort to maintain a program is larger in this environment.

79. The range of database applications can be divided into five categories. Explain the five different categories.

Ans: Databases can support from a single user (personal database) up to supporting the requests of the world (internet database). In between, a database can support a workgroup (a relatively small group of people), department database (a functional unit in an organization such as marketing), or an enterprise database (entire organization).

80. Explain the differences between an intranet and an extranet.

Ans: An Internet database is accessible by everyone who has access to a Web site. An intranet database limits access to only people within a given organization. An extranet database limits access to only people within a company and a company's customers and suppliers.

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81. Briefly explain the five components of an Information Systems Architecture and their relationship to data.

Ans: Processes that manipulate the data. Networks that transport the data. People who process and use the data. Events and point in time when processes need to be performed with the data. Reasons for events and rules to govern the processing of the data.

82. Explain the systems development life cycle.

Ans: This is the traditional method to develop, maintain, and replace information systems that includes the project identification and selection, project initiation and planning, analysis, logical design, physical design, implementation, and maintenance steps. The process is a series of steps that are ideally completed in a linear fashion. In reality, the process is not linear and the process requires steps to be revisited and an overlap of steps.

83. Explain the differences of the two principal types of packaged data models.

Ans: Universal data models are common to many organizations. These models may be useful for similar functions that are used across companies or organizations such as purchasing and accounting. Industry-specific data models are used by specific industries.

84. Who can make up a systems or database team? Provide a brief explanation of each.

Ans: The team includes a system analyst who identifies the need for information services to meet opportunities of the business, database analysts who design the database, users who monitor that the system will meet their needs, programmers who write computer programs, database and data administrators who have responsibility for current and future databases and other technical experts.

85. Briefly describe the six database activities that occur during the systems development life cycle.

Ans: The enterprise modeling that analyzes the current data processing. Conceptual data modeling that identifies entities, relationships, and attributes. The logical database design that identifies data integrity and security requirements. The physical database design and definition that defines the database to a DBMS. The database implementation that installs and converts data from prior systems. Database maintenance that fixes errors in the database and database applications.

86. Briefly explain an ERD.

Ans: An ERD is a detailed logical representation of the data for an organization. The ERD includes entities, attributes, relationships, and cardinalities. An ERD is the mechanism where an entity-relationship model is displayed.

87. List some of the chrematistics of good data definitions.

Ans: Definitions are gathered from the same sources and should be accompanied diagrams. A definition will include special conditions, examples, how the data is created, whether the data can change, who owns the data, whether the data is optional, and whether the data can be broken into something more atomic.

88. Explain minimum and maximum cardinality.

Ans: Minimum cardinality is the minimum number of instances of an entity that can be associated with each instance of another entity. Maximum cardinality is the maximum number of instances of an entity that can be associated with each instance of another entity.

89. Describe the naming of Relationships?

Ans: Relationships are verb phrases and represent actions usually in the present tense. The name should exclude vague names such as "has". The name should explain what action is being taken and possibly why it is important.

90. Why is modeling time-dependent data with a time stamp important?

Ans: The values of data may change. A time stamp helps to ensure that the previous value of the data stays in the database after it has changed so that you can see the before and after values through time. Without a time stamp, you will most likely lose some of the history.

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91. Explain the difference between total specialization and partial specialization.

Ans: Total specialization exists when every instance of a supertype must also be an instance of a subtype. Partial specialization exists when every instance of a supertype does not have to be an instance of a subtype.

92. Explain the difference between an ERD and EER.

Ans: An EER includes everything in an ERD and an EER allows for more complex relationships than an ERD. An EER allows for object-oriented data modeling and include supertypes and subtypes entities and inheritance.

93. Explain the difference between the disjoint and overlap rule.

Ans: The disjoint rule states an entity instance of a supertype can only be a member of one subtype. The overlap rule states an entity instance of a supertype can be a member of multiple subtypes.

94. List the three types of business rules and define each of them.

Ans: A derivation is a statement that is derived from other knowledge. A structured assertion is a statement that expresses some aspect of the static structure of an organization. An action assertion is a statement of a constraint on the actions of an organization.

95. Explain how a scenario is used for business rules.

Ans: A scenario is used to test business rules. It is a short script that describes how a business reacts to certain situations.

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96. Explain some of the main goals of normalization.

Ans: Normalization should minimize data redundancy. It should also simplify referential integrity constraints. Normalization will also make it easier to insert, update, and delete data. And finally, it provides better design.

97. List some of the properties of a relation.

Ans: Relations in a database have a unique name and no multivalued attributes exist. Each row is unique and each attribute within a relation has a unique name. The sequence of both columns and rows is irrelevant.

98. Explain what needs to happen to convert a relation to third normal form

Ans: First you must verify that a relation is in both first normal form and second normal form. If the relation is not, you must convert into second normal form. After a relation is in second normal form, you must remove all transitive dependencies.

99. Describe how a supertype/subtype relationship is mapped into a relation.

Ans: A separate relation is created for each supertype and subtype. The attributes common for all of the subtypes are assigned to the supertype. Each subtype has the primary key from the supertype assigned to it. A subtype discriminator is added to the supertype.

100. Describe domain constraints.

Ans: Domain constraints include entity integrity and referential integrity. The domain is a set of values that may be assigned to an attribute. The entity integrity rule states that no part of a primary key cannot be null. Referential integrity states that each foreign key value must match a primary key value or be null.