Hierarchy of Data
Data is organized in layers. In the computer profession, data is classified in a hierarchy. Each higher level of data consists of one or more items from the lower level. Depending on the application and the user, different terms describe the various levels of the hierarchy.
Characters
In the ASCII coding scheme, each byte represents a single character, which can be a number (4), letter (R), space, punctuation mark (?), or other symbol (&).
Fields
A field is a combination of one or more related characters or bytes and is the smallest unit of data a user accesses. A field name uniquely identifies each field. The field size defines the maximum number of characters a field can contain.
Data is organized in layers. In the computer profession, data is classified in a hierarchy. Each higher level of data consists of one or more items from the lower level. Depending on the application and the user, different terms describe the various levels of the hierarchy.
Characters
In the ASCII coding scheme, each byte represents a single character, which can be a number (4), letter (R), space, punctuation mark (?), or other symbol (&).
Fields
A field is a combination of one or more related characters or bytes and is the smallest unit of data a user accesses. A field name uniquely identifies each field. The field size defines the maximum number of characters a field can contain.
The data type specifies the kind of data a field can contain and how the field is used. Common data types include:
• Text (also called alphanumeric) — letters, numbers, or special characters
• Numeric (also called number) — numbers only
• Auto Number — unique number automatically assigned by the DBMS to each added record
• Currency — dollar and cent amounts or numbers containing decimal values
• Date (also called date/time) — month, day, year, and sometimes time
• Memo — lengthy text entries
• Yes/No — only the values Yes or No (or True or False)
• Hyperlink — E-mail address or Web address that links to a Web page on the Internet or document on a local network
• Object — photo, audio, video, or a document created in other programs and stored as a bitmap in the database
• Attachment — document or image that is attached to the field, which can be opened in the program that created the document or image (functioning similarly to e-mail attachments)
Records
A record is a group of related fields. For example, a student record includes a set of fields about one student. A primary key is a field that uniquely identifies each record in a file. In some tables, the primary key consists of multiple fields, called a composite key.
Files
A data file is a collection of related records stored on a storage medium such as a hard disk or optical disc. A database includes a group of related data files.
• Text (also called alphanumeric) — letters, numbers, or special characters
• Numeric (also called number) — numbers only
• Auto Number — unique number automatically assigned by the DBMS to each added record
• Currency — dollar and cent amounts or numbers containing decimal values
• Date (also called date/time) — month, day, year, and sometimes time
• Memo — lengthy text entries
• Yes/No — only the values Yes or No (or True or False)
• Hyperlink — E-mail address or Web address that links to a Web page on the Internet or document on a local network
• Object — photo, audio, video, or a document created in other programs and stored as a bitmap in the database
• Attachment — document or image that is attached to the field, which can be opened in the program that created the document or image (functioning similarly to e-mail attachments)
Records
A record is a group of related fields. For example, a student record includes a set of fields about one student. A primary key is a field that uniquely identifies each record in a file. In some tables, the primary key consists of multiple fields, called a composite key.
Files
A data file is a collection of related records stored on a storage medium such as a hard disk or optical disc. A database includes a group of related data files.