Database Dictionary
Provided by GeekGirls.com
http://www.geekgirls.com/database_dictionary.htm
database: A collection of
related information stored in a structured format. Database is sometimes
used interchangeably with the term table. Technically, they’re
different: A table is a single store of related information; a database can
consist of one or more tables of information that are related in some
way. For instance, you could track all the information about the students in a
school in a students table. If you then created separate tables containing
details about teachers, classes and classrooms, you could combine all four
tables into a timetabling database. Such a multi-table database is called a relational
database.
data entry: The process of getting information into a
database, usually done by people typing it in by way of data-entry forms
designed to simplify the process.
dbms: Database management system. A program which lets you manage information
in databases. Lotus Approach, Microsoft Access and FileMaker
Pro, for example, are all DBMSs, although the term is often shortened to
‘database’. So, the same term is used to apply to the program you use to organize
your data and the actual data structure you create with that program.
field: Fields describe a single aspect of each member of a table. A student record, for instance, might
contain a last name field, a first name field, a date of birth field and so on.
All records have exactly the same structure, so they contain the same fields.
The values in each field vary from record to record, of course. In some
database systems, you’ll find fields referred to as attributes.
flat file: A database that consists of a
single table. Lightweight database programs such as the database
component in Microsoft Works are sometimes called ‘flat-file managers’ (or list
managers) because they can only handle single-table databases. More powerful
programs, such as FileMaker Pro, Access, Approach and Paradox, can handle
multi-table databases, and are called relational database managers, or RDBMSs.
foreign key: A key used in one table to represent the value of a primary key in a related table.
While primary keys must contain unique values, foreign keys may have duplicates.
For instance, if we use student ID as the primary key in a Students table (each
student has a unique ID), we could use student ID as a foreign key in a StudentCourse
table: as each student may do more than one course, the student ID field in the
StudentCourse table (often shortened to StudentCourse.student ID) will hold
duplicate values.
index: A summary table which lets you quickly look up the
contents of any record in a table. Think of how you use
an index to a book: as a quick jumping off point to finding full information
about a subject. A database index works in a similar way. You can create an
index on any field in a table. Say, for example, you have
a customer table which contains customer numbers, names, addresses and other
details. You can make indexes based on any information, such as the customers’
customer number, last name + first name (a composite index based on more than
one field), or postal code. Then, when you’re searching for a particular
customer or group of customers, you can use the index to speed up the search.
This increase in performance may not be noticeable in a table containing a
hundred records; in a database of thousands of records it will be a blessing.
key field: You can sort and quickly retrieve information from a database by choosing one or more fields to act as keys.
For instance, in a students table you could use a combination of the last name
and first name fields (or perhaps last name, first name and birth dates to
ensure you identify each student uniquely) as a key field. The database program
will create an index containing just the key field contents.
Using the index, you can quickly find any record by typing in the
student’s name. The database will locate the correct entry in the index and
then display the full record.
Key fields are
also used in relational databases to maintain the
structural integrity of your tables, helping you to avoid problems such as
duplicate records and conflicting values in fields (see primary key and foreign key).
normalization: The process of
structuring data to minimize duplication and inconsistencies. The process
usually involves breaking down a single table into two or more
tables and defining relationships between those tables. Normalization is
usually done in stages, with each stage applying more rigorous rules to the
types of information that can be stored in a table. While full adherence to normalization
principles increases the efficiency of a particular database, the process can
become so esoteric that you need a professional to create and understand the
table design. Most people, when creating a database, don’t need to go beyond
the third level of normalization, called third normal form.
primary
key: A field that uniquely identifies a record in a table. In a
students table, for instance, a key built from last name + first name might not
give you a unique identifier (two or more Jane Does in the school, for
example). To uniquely identify each student, you might add a special Student ID
field to be used as the primary key.
query: A view of your data showing information from one or more
tables. For instance, you could query the Students database asking "Show
me the first and last names of the students who take both history and geography
and have Alice Hernandez as their advisor" Such a query displays
information from the Students table (firstname, lastname), Courses table
(course description) and Advisor table (advisor name), using the keys (student
ID, course ID, advisor ID) to find matching information.
rdbms: Relational database management system. A program which lets you
manage structured information stored in tables and which can handle databases consisting of multiple tables.
record: A record contains all the information about a single ‘member’ of a
table. In a students table, each student’s details (name, date
of birth, contact details, and so on) will be contained in its own record.
Records are also known as tuples in technical relational database parlance.
relational database: A database consisting of more than one table. In a multi-table
database, you not only need to define the structure of each table, you also
need to define the associations between each table in order to link those
tables correctly.
report: A form designed to print information from a database
(either on the screen, to a file or directly to the printer).
SQL: Structured Query Language (pronounced sequel in
the US; ess-queue-ell elsewhere). A computer language designed to organize
and simplify the process of getting information out of a database in a usable
form, and also used to reorganize data within databases. SQL is most often used
on larger databases on minicomputers, mainframes and corporate servers.
table: A single store of related information. A table consists of
records, and each record is made up of a number of fields. Just to totally confuse things, tables are sometimes called relations.
You can think of the phone book as a table: It contains a record for each
telephone subscriber, and each subscriber’s details are contained in three
fields – name, address and telephone.