From andyt@cs.wisc.edu Mon Jul 22 09:15:38 1996 Received: from andvari.cs.wisc.edu (andvari.cs.wisc.edu [128.105.66.42]) by ricotta.cs.wisc.edu (8.6.12/8.6.12) with ESMTP id JAA16476 for ; Mon, 22 Jul 1996 09:15:36 -0500 Received: (from andyt@localhost) by andvari.cs.wisc.edu (8.6.12/8.6.12) id JAA10732; Mon, 22 Jul 1996 09:15:35 -0500 Date: Mon, 22 Jul 1996 09:15:35 -0500 (CDT) From: Andy Therber To: Raghu Ramakrishnan Subject: I fixed a help file Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO Here's a better version of the help file for the Session window: ************************************ * NEW TOPIC: The session window ************************************ designview Help: Session Window ============================ designview provides you with full display and editing capabilities for all decompositions specified in the process of schema refinement. Each source relation in your database can have one or more decomposition sessions associated with it, and within a session the source relation can be decomposed into new, "derived" relations. The derived relations can be decomposed further within the same session, or new sessions can be created for derived relations. IMPORTANT: Any time you try to create a derived relation that has an attribute set identical to a relation that already exists, designview will ask you to make a choice about how the new relation should be created. You can either create a brand new relation with the same attribute set as the other relation, but with a separate identity--any sessions associated with the old relation will not be associated with the new one. The other option is to use the previously existing relation in the decomposition that is currently being created. This will bring the name and associated sessions of the old relation into the session you are currently working on. Whenever a relation (source or derived) has more than one session, one of the sessions is chosen to be the "default" session. The default session is always the session at the top of any list of sessions, and it is the default session that gets used in the process of displaying all base relations. When you select a source relation in the main window, a list of its decomposition session appears. You can view one of these sessions by double-clicking on the session name or selecting "View Session" from the Session menu. You can also start a new session by selecting "New Session" from the Session menu. Once you have displayed a session, the menus in the session window allow you to perform these operations: * Save or rename the session. * Test a relation for BCNF/3NF. * Automatically decompose a relation into BCNF or 3NF. * Start a new decomposition session for a relation. * Link a relation to another session. * Undo decompositions within the session. * Hide or unhide attribute lists in the session tree. Here is a description of how to perform each of these operations: NOTE: If you click on a relation name in the session window, that relation becomes the active relation in the session. You then have the ability to perform various operations on the active relation through the operations in the Relation menu. * Save or rename the session. Select Save from the File menu to create a permanent copy of the current session. Select "Save As" to make a copy of the session under a different name. NOTE: "Save As" makes a copy of the session, the copy with the old name is not deleted. * Test a relation for BCNF/3NF. After highlighting a relation, you can test the relation for BCNF and 3NF through the "Test/Decompose" option in the Relation menu. If violations exist, you will be presented with a list of the violations, and you can respond in one of three ways: 1. Do nothing. Just click on the Dismiss button. 2. Decompose to remove a violation. Select a violation from the list, then click on the Decompose button. You will be warned if the generated decomposition is not dependency preserving or is not a lossless join decomposition. If a warning is displayed, you can cancel the decomposition by clicking on the Cancel button. Otherwise, the decomposition is performed and the derived relations are displayed in the session window. 3. Perform a custom decomposition. If you click on the "Custom Decomposition" button, a window will appear in which you can define a new decomposition for the active relation. At the top of the decomposition window is a list of all attributes in the original relation. And across the bottom half of the window is a set of frames which will display the attribute sets for all relations in the decomposition. I'll refer to the original relation as the "parent" relation, and all derived relations as "children". To copy attributes to a child relation, first go to the parent's attribute list and highlight the attributes to be copied. Then click on the Add button in the appropriate child frame. You can also delete attributes from a child by highlighting part of the child's attribute list and clicking on the Delete button. If you want to add a child frame, select "Add Child" from the Decompose menu. To delete a frame, click somewhere in the frame (the frame border will become a thick, solid black outline), and then select "Delete Child" from the Decompose menu. You can generate a BCNF or 3NF decomposition by selecting "Generate BCNF" or "Generate 3NF" from the Decomposition menu. And at any time while working on your decomposition, you can test for Lossless Join and Dependency Preservation through the Test menu. Once you are satisfied with your decomposition, click on the Done button and the decomposition will be added to the session. Clicking on the Cancel button discards all work you have done in the decomposition window. * Automatically decompose a relation into BCNF or 3NF. Another option under the "Test/Decompose" item of the Relation menu is to automatically generate a decompostion that puts your relation into a chosen normal form (BCNF or 3NF). If the relation in already in the chosen normal form, you will be informed of this and no decomposition will be performed. * Start a new decomposition session for a relation. Select "New Session" from the Relation menu to open a new session window for the active relation. * Link a relation to another session. Within a specific session, you can create a link between one of the relations in that session and some other session which has that relation as its root. If you select "Link to Another Session" from the Relation menu you will be shown a list of other decompositions defined for the highlighted relation. Selecting one of these other sessions establishes it as the "linked session" for the highlighted relation. These session links are followed when you ask designview to generate SQL statements for all base relations in your database. Once a linked session has been defined for a relation, its name will appear in the linked session button below the session tree. Clicking on this button will bring up a session window for the linked session. If you have not defined a linked session for the relation that is highlighted in the session window, then no text will appear in the linked session button, and clicking on the button has no effect. * Undo decompositions within the session. Once a relation has been decomposed within a given session, you can delete all of the derived relations below the active relation by selecting "Undo Decomposition" from the Relation menu. WARNING: Deleting a derived relation which has decomposition sessions associated with it results in all the sessions being deleted also. * Hide or unhide attribute lists in the session tree. Within the session tree you have the ability to hide and unhide the attribute list of any relation. By double-clicking on a relation name you toggle the relation between hiding and displaying its attribute lists. Options also exist in the View menu for performing hide/unhide operations over the entire tree.