There are several predefined types of attributes.

Standard Attributes
Text

Description: A text field is an input that allows a user to write or edit text. Single-line, up to 255 characters.
Sorting: alphabetically
Filtering:
- is equal to
- is not equal to
- starts with
- contains
- dos not contain
- ends with
- is null
Long Text

Description: A text field is an input that allows a user to write or edit text. Multi-line, unlimited characters.
Sorting: alphabetically
Filtering:
- is equal to
- is not equal to
- starts with
- contains
- dos not contain
- ends with
- is null
Email

Description: An attribute to store the email address. Contains standard validation of the email address.
Sorting: alphabetically
Filtering:
- is equal to
- is not equal to
- starts with
- contains
- dos not contain
- ends with
- is null
Number

Description: An attribute to store a number – integer/float, positive/negative.
Sorting: numerically
Filtering:
- greater then
- greater than or equal to
- is equal to
- less than
- less than or equal to
- is null
Date

Description: An attribute to select a date from the calendar.
Sorting: by absolute time
Filtering:
- is equal to
- is not equal to
- is after or equal to
- is after
- is before or equal to
- is before
- in range
- is null
- is not null
Linkers
The following are the attributes that allow a user to link an entry or to display the particular 'external' links in read-only mode.
Directory

Description: Gives users the ability to make multiple selections from a number of options (entries of the particular directory). Read more: Interlink Catalog Objects
Sorting: n/a
Filtering: as a select-list (via OR)
Linked Catalog Entries

Description: Displays Catalog entries linked to the current entry via Directory attribute(s). Read more: Interlink Catalog Objects
Sorting: n/a
Filtering: as a select-list (via OR)
Linked Issues

Description: A read-only attribute that displays issues linked to the current entry via Catalog Select custom field(s). Read more: Link Issues And Catalog Objects
Sorting: n/a
Filtering: as a select-list (via OR)