CIS 250 Advanced Computer Applications Database Management Systems

University of South Alabama - CIS 2502 Databases Used to store electronic information Referred to as secondary storage We will discuss Uses for databases How information may be organized in databases How it may be processed

University of South Alabama - CIS 2503 Data Organization Character – a single letter, number, or character (ex: A) Field – a set of related characters (ex: Last Name) Record – a set of related fields (ex: all information on a specific drivers license) Table – a collection of related records (ex: all drivers licenses for Mobile County) Database – a collection of related files (ex: all drivers license files for the state of Alabama)

University of South Alabama - CIS 2504 Key Fields Key fields are used within each record to specifically identify an individual record Should be unique Example: driver’s license number

University of South Alabama - CIS 2505 Processing of Data Batch processing - data is collected over a period of time (hours, days, or weeks, etc.) and is processed all at once Real-time processing - data is processed at the same time the transaction occurs; more widely used now due to direct access storage (disks)

University of South Alabama - CIS 2506 File Organization 3 main methods of file organization: Sequential Direct file storage Index Sequential

University of South Alabama - CIS 2507 Sequential File Storage Sequentially - records are stored physically one after another in a predetermined order, determined by the key field; can be stored on tapes. Advantage - can be very efficient when all or large portions of the records need to be accessed at the same time Disadvantage - can be much slower when looking for a particular record since we must begin with the 1st record and check through every one in order until we find it

University of South Alabama - CIS 2508 Direct file storage Direct file storage - records are stored on a disk in a particular address that can be determined by their key field; can be stored on disk. Adv - very efficient when finding a specific record and does not require looking through each one in order to access it Disadv - more storage space is required on the disk, which may not be as good when accessing large portions of the record.

University of South Alabama - CIS 2509 Index sequential Index sequential access - a compromise between sequential and direct file access; Records are stored in a file, in sequential order; however, an index also exists. The index lists the key to groups of records and the corresponding disk address for those records. Requires disks as storage devices.

University of South Alabama - CIS Index sequential (cont) Adv - faster than sequential, but not as fast as direct file access for specific records; when updating a large number of records, it is faster than direct access but slower than sequential access. Best used when large amounts of records must be updated only occasionally, but the user also desires quick access to specific records.

University of South Alabama - CIS Benefits of Databases Data Sharing – information in one department can be readily shared with other departments. Security – users can be given passwords and/or access only to the kind of information they need to know while containing all of the information only once in the database. Data Redundancy – fewer files are necessary; the data is stored only once and in one location. This reduces the storage space needed. Data Integrity – Changes made in the file will update all occurrences of the information.

University of South Alabama - CIS Database Management Systems DBMS - special software that allows you to create, modify, and gain access to a database. data dictionary - contains a description of the structure of the data used in the database; defines the field names, what type of data can go into the field, the size of the field, and also defines which field is the key field. query language - allows access to the information in the database; most widely used query language is SQL (structured query language).

University of South Alabama - CIS Database Organization Most common types of database formats are: Hierarchical Database Network Database Relational Database Object Oriented Database

University of South Alabama - CIS Hierarchical Databases Structured in nodes (tree like structure) Each child node has one and only one parent node (a parent may have more than one child node). We refer to this as a 1-to-many relationship. Progress top down to traverse fields. To find information, you must start at the top with a parent node and trace down the tree. Use pointers to connect parent node to child nodes.

University of South Alabama - CIS Hierarchical Databases Advantages of Hierarchical Databases: Efficient and easy to create Disadvantages of Hierarchical Databases: If a parent node is deleted, so are all child nodes Cannot add a child node without adding all parent nodes first Low flexibility – paths and directories to information must be specified in advance; very difficult to change Difficult to maintain

University of South Alabama - CIS Network Databases Variation on the hierarchical database to reduce data redundancy Child nodes can have more than one parent (many-to-many relationship) Nodes are reached through pointers; may provide more than one path to same information

University of South Alabama - CIS Network Databases Advantages of Network Databases: Efficient Faster than hierarchical Less data redundancy Disadvantages of Network Databases: Low flexibility More pointers; the number of pointers increases rapidly, which makes it much more complicated to maintain and operate.

University of South Alabama - CIS Relational Databases The most flexible – it is not hierarchical in nature Uses tables made up of columns and rows Columns correspond to Fields Rows correspond to Records Related tables can be linked together through Common Data Elements (keys, foreign keys)

University of South Alabama - CIS Relational Databases Advantages of Relational Databases: Simple to add, delete, and edit; there are no pointers It can relate data in one field in one table to another field in another table Flexible – ad hoc queries can combine data from different sources Disadvantages of Relational Databases: Slower – may require multiple access to the data Requires some data redundancy in order to be more efficient - the same data must appear in multiple tables to link the tables Must remember to change/update all tables

University of South Alabama - CIS Object Oriented Databases  Handles unstructured data such as photographs, graphics, audio, video, etc.  Keep track of objects – both data and the action that can be taken on the object.

University of South Alabama - CIS Types of Databases Individual – collection of files primarily used by just one person Company/Shared – databases that can be used by multiple users, shared through local area networks Distributed – data for the database is stored in multiple locations with access through communication networks Proprietary – an enormous database developed to cover particular subject areas; usually offers access to people for a fee – databanks.

CIS 250 Advanced Computer Applications Database Management Systems