Databases

What are ways of doing cross-reference in a database?

"Associative Linking" is how tables are linked. Relational database rests heavily on associative linking rather than pointing: •Notice distinction above between referring to places or to place-occupants: i.e., where or what, respectively ... •Pointing or associative linking, respectively. •Your party-attendance plan for the month would use Pointing: if it referred to the party-givers by position, e.g. by page and line number in your address book, Associative Linking: if it referred by means of party-givers' names. Labels in a diagram are a means for associative linking between the diagram and the legend (= explanation of the labels, etc.) or other text.

What are the advantages of a DBMS compared to File System Data Management?

1. Data Redundancy. •Replicating data in different places in a data repository. (E.g. student data is replicated in several department files). •Data inconsistency: different and conflicting versions of same data occur at different places •Data anomalies: abnormalities when all modifications/changes in redundant data not made correctly •Update anomalies •Insertion anomalies •Deletion anomalies 2. Structural and data dependence. Unlike in databases which store data as well as metadata (catalog), file systems store data only. The structure of the data is stored in the application that access the file. •Structural dependence: changing the file structure requires changing the application that access that file. •E.g. adding student DoB field. •Data dependence: data access changes when data storage characteristics change •E.g changing a data field from integer to character. Structural and data dependence make file systems very difficult to manage - High Maintenance. Other Problems: •Poor design and lack of standardized data modeling •Security features difficult to program •Requires extensive programming to perform ad hoc queries •System administration complex and difficult •Difficult and expensive to integrate various applications. •Impossible to have multiple people or applications working on the same file. A DBMS has: •Improved data sharing •Improved data security •Better data integration •Minimized data inconsistency •Improved data access •Improved decision making •Increased end-user productivity.

What are the characteristics of a Relational Table?

A table is perceived as a two-dimensional structure composed of rows and columns. Each table row (tuple) represents a single entity occurrence within the entity set. Each table column represents an attribute, and each column has a distinct name. Each row/column intersection represents a single data value. All values in a column must conform to the same data format. Each column has a specific range of values known as the attribute domain. The order of the rows and columns is immaterial to the DBMS. Each table must have an attribute or a combination of attributes that equally identifies each row.

What is the difference between data and information.

Database is a collection of logically coherent interrelated data as well as a description of this data. Information is the result of processing data to reveal its meaning. Data are raw facts •Information produced by processing raw data to reveal meaning •Data are the foundation of information, which is the base of knowledge •Raw data must be structured for storage, processing, and presentation •Database technology provides the most efficient data management. •Database technology is crucial for good decision making.

What are the restrictions on database tables?

Overall Structure •Regular overall shape: rows all same length, similarly columns. •No division into different regions (with a certain exception). •No labels for rows, as opposed to columns. •Mostly no significance to the order of rows. •No additional comments, footnotes, etc. Nature of Entries •All cells in any one column are given the same intuitive interpretation. •Each cell's item restricted to a pre-specified, usually fairly simple value range (data type), and all cells in any given column restricted to same data type. •No exceptional entries ... with one exception!: empty entries •One data item per cell (but it can be a variable-length character string, containing anything). •Uncertainty and vagueness markers not supported. Extra, Crucial Restriction (on the main tables) •No row can be repeated in a table. (I.e., no two rows can contain exactly the same values.) •This is equivalent to saying: Rows are uniquely determined (picked out) by the values in some set of columns (possibly the whole set, but could be fewer). That is, if you imagine some values for those columns, there is at most one row that has exactly those values in those columns.

What are the languages of the DBMS?

The Data Definition Language (DDL) •used by Database Administrator (DBA) •used to describe/create external and logical schema The Data Manipulation Language (DML) •used to retrieve, insert, delete and modify data •used interactively or embedded in a programming language

What is a Database?

The broad interpretation of a Database = A collection of logically coherent interrelated data (raw facts of interest to the end user) + Description of data characteristics and relationships (Metadata: data about data).

What is a Database Management System (DBMS)?

•A Database Management System (DBMS) is a software system designed to: •Define and create the database structure •Manage and manipulate data •Control access to database •DBMS is the intermediary between the user and the database.

What is the difference between Databases, Database Management Systems and Database systems.

•A database (DB) consists of a DB schema and a DB state. •A database management system (DBMS) is a collection of programs that manage the database structure and control access to database. •A database system (DBS) consists of a DBMS and a database.

What is the definition of a database?

•A database is a structured body of information about entities of various specific, precisely defined types. •Generally there are many entities of at least some of the types •The entities are generally in various specific types of relationship to each other. •Each entity has a specific set of (intrinsic) attributes of interest. Their values are generally of fairly basic, simple sorts (e.g., numbers, dates, names). •The entities of a given type are typically not in any special order other than an order arising naturally from their attributes. •The individual data elements held are directly meaningful & interesting to such users •The data held and retrieved is generally of exact form (no vagueness expressed) and of definite form (no uncertainty expressed or expected). •The operations provided to users for extracting, inserting and updating data are of conceptually straightforward sorts, not requiring elaborate reasoning, problem-solving or analysis. •However, aggregate/overview/statistical information (counts, averages, maxima, etc.) often needs to be computed from the data.

What are the different types of database?

•Databases can be classified according to various aspects, for example: 1. Number of users •Single-user database: supports only one user at a time •Desktop database •Multi-user database: supports multiple users at the same time •Workgroup database •Enterprise database 2. Database location(s) •Centralized database: data located at a single site •Distributed database: data distributed across several different sites 3. Time sensitivity •Operational database: supports a company's day-to-day operations •Online Transaction Processing •Analytical database: stores data used for tactical or strategic decisions •Data warehouse 4. Type of data stored in •General purpose database •Discipline specific database

Describe the 5 major parts of a database system?

•Five major parts of a database system: Hardware, Software, People, Procedures & Data. •Organization of components that control the collection, storage, management and use of data.

What are the disadvantages of using character strings as linking values?

•In entering values, have to ensure exactly the same string of characters on each occasion •avoid typos e.g. "Finance", "Finace" •Inefficiency of comparing such complex values. Reduce such problems by: •Using artificial linking values that are simpler in form and easier to make distinct .....

What is Referential Integrity?

•Referential integrity is relevant when one place in a data repository needs to refer to something in another place: cross-references. •Referential integrity is achieved when every such referring place contains a successful reference to another place or place-occupant (or no reference at all). •"Successful" there just means that the reference succeeds in specifying some other place(-occupant).