What is Program-Data Redundancy?
changing the structure or storage characteristics would require changing the applications that access it
Unnecessary storage of the same data in different places
different and conflicting versions of the same data occur at different places
Abnormalities when all changes in redundant data are not made correctly
What is Data Redundancy?
What is Data Inconsistancy?
What is Data Anomalies?
Data Dictionary Management - Data dictionary: Stores of the and their
- Performance tuning: Ensures of the in terms of and access
- Transforms entered data to conform to required data structures
- Enforces user security and data privacy
- Sophisticated algorithms ensure that multiple users can access the database concurrently without compromising its integrity
- Enables recovery of the database after a failure
- Minimizes redundancy and maximizes consistency
interfaces - Query language: Lets the user specify what must be done without having to specify how • Structured Query Language (SQL): De facto query language and data access standard supported by the majority of DBMS vendors
- Accept end-user requests via multiple, different network environments
Abstraction of a real-world object or event is an example of Data Models?
Collection of related concepts used to describe the structure of a database, i.e. unique objects, data types, relationships, and constraints • Useful for supporting a specific problem domain • Simple representations of complex real-world data structures
This is an example of Data Modelling
A Model refers to the process of creating a specific data model for a determined problem domain.
An is a person, place, thing, or event about which data will be collected and stored.
An is a characteristic of an entity
A describes an association among entities.
A is a restriction placed on the data
• Logical Data Independence:
Change the schema at one level of a database system without having to change the schema at the next higher level.
A change in storage devices or methods and even a change in operating system will not affect the internal model.
Change the internal model without affecting the conceptual model.
Change the physical model without affecting the internal model
Recoding, adding fields (e.g. adding an email address to a student file) in the database should not affect applications
Data Independence:
Physical Data Independence:
- An attribute that can identify each row in a table uniquely. Cannot be null or duplicate
- Composed of more than one attribute
- Unique key other than primary key, Strictly for data retrieval purposes, E.g. Customers do not remember their ID, but they do remember their phone number!
- Each row (entity instance) in the table has its own unique identity
- An attribute whose values match primary key values in the related table
- FK contains a value that refers to an existing valid tuple (row) in another relation
will show all rows in the tables except duplicates
will show all rows from the tables including duplicates
- Unary operator that yields a vertical subset of a table. Yield all values for selected attributes
- Yields only the rows that appear in both tables
- Yields all rows in one table that are not found in the other table
: one or more attributes that uniquely identify each entity instance.
: Attribute that can be subdivided to yield additional attributes
: Attribute that cannot be subdivided
: Attribute that has only a single value.
s: Attributes that have many values.
: Attribute whose value is calculated from other attributes
