Database Systems Overview

Database Systems

• The first general purpose DBMS was designed by Charles William Bachman III at General Electric
• The DBMS, called Information Management System (IMS), formed the basis for an alternative data representation framework called the hierarchical data model
• Data is defined as raw facts
• Data management is a discipline that focuses on the proper generation, storage, and retrieval of data
• End-user data is defined as raw facts of interest to the end-user
• Metadata is data about data and helps integrate and manage end-user data
• A workgroup database is a multiuser database that supports a relatively small number of users (usually fewer than 50) or a specific department within an organization
• An enterprise database is used by the entire organization and supports many users (more than 50, usually hundreds) across many departments
• A centralized database supports data located at a single site
• Bitcoin is an example of a decentralized database system
• A field is a character or group of characters (alphabetic or numeric) that has a specific meaning and is used to define and store data
• A record is a logically connected set of one or more fields that describes a person, place, or thing
• A file is a collection of related records
• Atomicity is a property of a database transaction; it ensures that the transaction either completes entirely or fails entirely
• Data redundancy exists when the same data is stored unnecessarily at different places
• Data anomaly develops when not all of the required changes in the redundant data are made successfully
• Isolation means that the execution of all transactions should be isolated from other transactions
• Durability ensures that the changes made during a transaction should exist after completion of the transaction

Database Systems Components

• The five major components of a database system are hardware, software, people, data, and procedures
• DBMS software manages the database within the database system
• Data optimization relates to the activities that make the database perform more efficiently in terms of storage and access speed
• Data transformation and presentation is the function of DBMS that transforms entered data to conform to the required data structures
• Data integrity promotes and enforces integrity rules, thus minimizing data redundancy and maximizing data consistency
• Back-up and recovery management is the function of DBMS wherein a failed database can be recovered
• A schema is a description of data in terms of a data model
• There is only a single conceptual view of a single database

Database Design

• The ER diagram was first introduced in 1976
• NoSQL is a 4th generation data model
• An attribute is a characteristic of an entity
• A business rule is a brief, precise, and unambiguous description of a policy, procedure, or principle within an organization
• File system is the 1st Generation of Data Model
• Object-oriented/object-relational is the 4th Generation of Data Model

Relational Databases and NoSQL

• SQL engine executes all queries or data requests
• NoSQL models use schema-free or semi-structured approaches

Hierarchical, Network, and Relational Data Models

• The hierarchical data model is a model whose basic logical structure is represented by an upside-down tree
• The hierarchical model depicts a set of one-to-many (1M) relationships between a parent and its children segments
• The network model allows a record to have more than one parent
• Data Definition Language (DDL) enables the administrator to define the schema components
• The hierarchical model creates a hierarchical tree with a parent/child relationship, whereas the network model has graphs and links

Entity-Relationship Modeling

• The Entity relationship model uses graphical representations to model database components
• Relationships describe associations among data
• Crows foot notation is derived from the three-pronged symbol used to represent the "many" side of the relationship
• Chen's notation uses connections written next to each entity box, and relationships are represented by a diamond connected to the related entities through a relationship line
• Dependent entities rely upon the existence of other entities

UML Class Diagram

• UML class diagrams are used to represent data and their relationships within the larger UML object-oriented system's modeling language
• A class diagram is also known as a structural diagram
• The minus symbol (-) denotes private attributes or operations
• The hash symbol (#) denotes protected attributes or operations
• A conceptual model represents the concepts in the domain
• Specification focuses on the interfaces of Abstract Data Type (ADT) in the software
• Inheritance is a class relationship displayed as a solid line with a hollow arrowhead that points from the child element to the parent element
• Aggregation is a special type of association that represents a "part of” relationship
• Composition is a special type of aggregation where parts are destroyed when the whole is destroyed
• Dependency is a class relationship wherein an object of one class might use an object of another class in the code of a method
• Realization is a class relationship between the blueprint class and the object containing its respective implementation level details
• The physical schema describes the way data are saved on storage media such as disks or tapes
• Data normalization is a process for evaluating and correcting table structures to minimize data redundancies, thereby reducing the likelihood of data anomalies