Let's first start with Perspectives in designer 8.5.1.Perspective determines the visible actions and views within a window.It goes well beyond this by providing mechanisms for task oriented interaction with resources in the Domino designer, multi-tasking and information filtering.
Designer 8.1.1 user interface is built on Eclipse so it's now called Workbench. A Workbench window offers one or more perspectives. A perspective contains editors and views, such as the designer application.Multiple Workbench windows can be opened simultaneously. Initially, in the first Workbench window that is opened, the designer perspective is displayed, with only home page visible (or blank editor area). If by mistake you have closed all the perspectives you may get blank designer window which sometimes confuse you .Here is the example,
To get back your designer perspective go to window->Open Perspective->Other and choose Domino designer.
So, In simple words; A workbench is a visual container for a set of views and editors. The structure of the workbench is exposed within the following diagram. The workbench window is outlined in red. Within this window there is a single open perspective in blue.Editor area is in Pink and Green shows different views.
What is perspective ?
perspectives can exist in a single Workbench window. Each perspective contains one or more
views and editors. Within a window, each perspective may have a different set of views but all
perspectives share the same set of editors.
An editor is also a visual component within the Workbench. It is typically used to edit or
browse a resource. Modifications made in an editor follow an open-save-close life-cycle model.
Multiple instances of an editor type may exist within a Workbench window. In prior versions
of designer we use only one editor at a time but designer 8.5.1 (8.5 as well) allows you to open
more than one editor at the same time. So we can simultaneously preview form designer
while write code or designing views.
Depending on the type of file that is being edited, the appropriate editor is displayed in the editor area. For example, if a .css file is being edited, a style sheet editor is displayed in the editor area.
A view is a visual component within the Workbench. It is typically used to navigate a hierarchy of information (such as the resources in the Workbench), open an editor, or display properties for the active editor. Modifications made in a view are saved immediately. Normally, only one instance of a particular type of view may exist within a Workbench window.
A view might appear by itself or stacked with other views in a tabbed notebook.
It can be detached and placed on top of the other views ,
A view can be displayed by selecting it from the Window > Show Eclipse views menu. A perspective determines which views may be required and displays these on the Show View sub-menu. Additional views are available by choosing Other... at the bottom of the Show Eclipse Views sub-menu. This is just one of the many features that provide for the creation of a custom work environment.
There are some useful menu options which can be used if you lost in Eclipse UI .
1- To open existing perspective : If you work on Lotus and Java projects more often then it's good to have two perspective because some views are not compatible with each other for example "Outline" view. You can design custom perspective based on most useful and frequent options. To open existing perspective use Window->Open perspective->Other menu.
2- Customize perspective : To customize perspective as per your need go to Window->Customize perspective ,
3- Saving new perspective : If you have design your own custom perspective use Window->Save perspective as option to save for later use.
4- Reset perspective : It may happen if you messed up with your working perspective , Use Window->Reset perspective option to reset it.
5- Closing perspective : There are two options in this context one is to close all perspective and other to close perspective. Close perspective will only close currently active perspective where as close all perspective will close all the open perspectives and you will see blank screen as I've mentioned in the beginning.
However I feel there should be a button and text message ( like Eclipse ) to give better understanding and guide end user to next step.
(Note: below screen is my mock-up design )