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hierarchy of data in database systems
bits - bytes - fields - records - tables (files) - database
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a digit, or bit (in a binary system) can only have
2
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bits are combined together into 8-bit groups called
bytes
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a group of bytes or characters is called
field
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in a database table, fields are usually organized into
columns
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a group of fields makes up a
record
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in a database table, records are usually organized into
rows
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a group of records makes up a
table
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a group of records makes up a
database
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field formats (6)
- -numeric
- -currency
- -tax
- -date/time
- -autoNumber
- -Yes/No
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numeric
only stores numbers and it displays numbers the way they're entered
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currency
can store only numbers, but it displays and prints a $, compare
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text
can share any keyboard character
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date/time
display date and/or time in various ways
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AutoNumber
automatically numbers each record as it is entered, starting with #1
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Yes/No
field can only contain one of two values, such as yes/no, true/false, off/on- there is a checkbox
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primary key
every row in a table must be unique (different) from all other rows, or else it can't be retrieved easily when you search the database-- a column (or pair of rows) that makes each row different from all other rows
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composite primary key
combination of two or more fields that together serve as primary key to uniquely identify records in the table
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secondary keys
fields (other than primary key fields) that are used to identify groups of records- often used to sort records
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sequence coding system
records are numbered sequentially (0001, 0002..ect)
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block coding system
similar items are coded together using a range of items (chart of accounts)
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group coding system
each digit in the items code indicates something about the item
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Mnemonic coding system
digits used in the coding system help you understand and remember their meaning (ACCT, AMST)
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entity relationship (ER) diagrams
ER diagrams are primarily used when designing a database
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rectangles represent in ER diagrams
entities (objects and activities the company wants to keep track of)
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R =
E =
A =
- resources (assets)
- events (activities)
- Agents (people/organizations)
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