There are several different types of view, that are used to display and input data in different ways. They are:

• Views that just display data
• Views that define items
• Views that define ranked items
• Views that give information about the user
• Views that describe a single item
• Media gallery views.

Views that just display data simply display the rows of data values that satisfy their constraints in a table, with the rows underneath each other. They cannot be used to edit the data values or input new ones, or to request actions.

The rows of data are sorted by their values according to the sort priorities and sort directions of the view's unknowns.

Each row has a value for each of the view's unknowns. For example, in a view of people's first names, last names, and middle names, if a person has a first name and last name but no middle name, no data for that person is displayed.

An item definition view displays data about a particular type of item, and enables users to input and change data. Users can create new items, delete items, and change the data associated with an item. Users can request actions, and actions can be performed automatically when data is changed.

When an item definition view displays data, each row contains the data values relating to a particular item. The unknown that is the name of this item is the item definition unknown.

For example, an item definition view of people's names might have item definition unknown Person, other unknowns N, M and L, and constraints Person Has first name N, Person Has middle name M, and Person Has last name L. Each row then contains a person's first, middle and last names.

The view can have tabular or linear display type. With tabular display type, the rows are displayed vertically, underneath each other. With linear display type, they are displayed horizontally, side by side.

The rows of data are sorted by their values in accordance with the sort priorities and sort directions of the view's unknowns.

An item definition view can have a key.

An item definition view with a key defines an item type that can be used as the type of an unknown of another view.

When an item definition view has a key, each row has a value for each of the key unknowns, but need not have values for the other unknowns, For example, in a view of people whose key unknowns are first name, last name, and nickname, some rows might include a middle name, but in other rows it could be blank.

A ranked item definition view is like an item definition view. The difference is that its rows are not sorted by the values of its unknowns; their order is determined by users, who can use drag-and-drop to move them around.

The view is given an automatically assigned unknown, its rank unknown, that determines the row order. Its values are adjusted automatically when a user drags and drops a row.

Some views used by the system are ranked item definition views. They include the view used to display page assignments when a page is edited, and the views used to display view unknowns, constraints and columns on a view page.

A user information view gives information about the logged-in user who is displaying it, and enables the logged-in user to enter information about themself. Different users viewing the same user information view will see different data. It is a kind of item definition view. The user can add, edit and delete user-related items of information.

The rows of data are sorted by their values according to the sort priorities and sort directions of the view's unknowns.

A user information view has an unknown that names the user-related items. This is the user information unknown.

A user information view can have a key. If it does, then only the key unknowns need have values.

User information views are a good way to enable users to view and change their personal information.

A single item description view gives information about a particular item in the system. It allows that information to be created, changed or deleted, but does not allow the described item to be created or deleted.

The system uses an item definition view when a page is edited to enable the user to set or change the browser bar title. The user can add, change or delete a title. Deleting the title does not delete the page.

A single item description view has an unknown that represents the described item. This is the described item unknown.

When a single item description view is displayed, there will be at most one row. If there is no row, the user can add one. If there is a row, the user can change its values or delete it. This means that, for example, a page can only have one title.

A single item description view can have a key. If it does, then only the key unknowns need have values.

A media gallery view lets you display images or YouTube videos  with associated information such as titles and descriptions. The images are all scaled to the same size so that the display is neat and attractive. Users can 

• Add or delete media and associated information
• Change the media and edit their associated information
• Drag and drop media to rearrange the display.

A media gallery is a kind of ranked item definition view. It has a gallery exhibit unknown, which is its item definition unknown. Its values are items that represent gallery exhibits. It also has a media unknown, whose values are the images or references to YouTube videos. The view's constraints link the gallery exhibit unknown to the media unknown and to unknowns whose values are associated information such as titles and descriptions.

There are two types of media gallery: column and rows. 

In the column type of gallery, the gallery exhibits are in a single column. Each exhibit has the media at its left side, with the associated information to the right of it.

In the rows type of gallery, the images or videos are arranged in rows. Each is stacked vertically with its associated information, in the order of their columns in the view definition. You can, for example, put the title above or below the image or video by changing this order.

These arrangements are set by the CSS files referenced in the default template. You can change them by using a custom template and a custom CSS file.

A view key is a set of unknowns whose combined values identify a row. 

For example, in a view of people, first name, last name and nickname might be the key. First name and last name only would be a bad choice because occasionally two people have the same first name and the same last name. Nicknames can then be used to distinguish them.

If a view has a key, it is an error to add a row with the same key values as an existing row. When a keyed view is displayed, any rows with duplicated key values are highlighted.