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Elweven by four (DATABASE MANAGEMENT (advantages of a DBMS include: (•…

- - - - • A data definition language processor, which allows the database administrator to create or modify a data definition for mappings between external and conceptual schemas
      - • Validation of the definition provided to ensure the integrity of the metadata
      - • Prevention of unauthorized access to, or manipulation of, the metadata
      - • Interrogation and reporting facilities that allow the DBA to make inquiries on the data definition
    - - • Enhance documentation.
      - • Provide common validation criteria.
      - • Facilitate programming by reducing the needs for data definition.
      - • Standardize programming methods.
  - - - DBMS will typically accommodate multiple DDLs for several application programming languages compatible with the DBMS.
    - - will provide appropriate
        mappings between the external and internal schemas.
- - - - is a hierarchy of parent
        and child data segments
        
        this model uses
        parent-child relationships
        
        (one-to-many) mappings between
        record types represented by logical trees,
        
        data relationships are hierarchical, the database is easy to
        implement, modify and search
        
        registry in Microsoft Windows is an
        example of a hierarchical database
    - - basic data modeling
        construct is called a set
        
        set is formed by
        
        a member
        record type
        
        can have that role in more than one set, so a multiowner relationship is allowed
        
        a name
        
        owner record type
        
        can also be a member or owner in another set
        
        disadvantage of the network model is that such structures can be extremely complex and difficult to comprehend, modify or reconstruct in case of failure.
    - - definition of data structures, storage/retrieval operations and integrity constraints.
      - In such adatabase, the data and relationships among these data are organized in tables.
      - table is a collection of rows, also known as tuples, and each tuple in a table contains the same columns
        
        Columns, called domains or attributes,
        correspond to fields
        
        Tuples are equal to records in a conventional file
        structure
      - Relational databases are used in most common ERP Systems.
      - Relational tables have the following properties:
        
        • Values are atomic, i.e., a single unit that is irreducible
        
        • Each row is uniquely identifiable.
        
        • Column values are of the same kind.
        
        • The sequence of columns is insignificant.
        
        • The sequence of rows is insignificant.
        
        • Each column has a unique name.
      - relational model is independent from the physical implementation of the data structure and has many advantages over the hierarchical and network database models
      - With relational databases, it is
        easier:
        
        • For users to understand and implement a physical database system
        
        • To convert from OTHER DATABASE STRUCTURES
        
        • To implement projection and join operations (i.e., reference groups of related data elements not stored together)
        
        • To create new relations for applications
        
        • To implement ACCESS CONTROLS over sensitive data
        
        • To modify the database
      - key feature of relational databases is the use of normalization rules to minimize the amount of information needed in tables to satisfy the users’ structured and unstructured queries to the database.
        
        normalization rules include:
        
        • A given instance of a data object has only one value for each attribute.
        
        • Attributes represent elementary data items; they should contain no internal structure.
        
        • Each tuple (record) consists of a primary key that identifies some entity, together with a set of zero or more mutually independent attribute values that describes the entity in some way (fully dependent on primary key).
        
        • Any foreign key should have a null value or should have an existing value linking to other tables; this is known as referential integrity.