OPEN

The OPEN command is used to enter an existing database. The OPEN refers to an Interface name which is then used to "plug you into" the database.

Syntax:
                OPEN/options Application-Interface-name

                Notation standards              Options Answers

Options:
                A             -Open even though there are cycle errors - only to unload records
                P              -Open the procedure catalog, not the database
                R             -Open in read-only mode
                S              -Open for exclusive use
                X             -Suppress the command response
                Y             -Do not alter the command answers cells

Answers:
                Ctl.Ans1                =Zero
                Ctl.Ans2                =Zero
                Ctl.Ans3                =Zero

Notes:
An Application Interface is the only avenue by which you plug into any given database. When you compile a Database Definition a default Application Interface file is created. Alternatively, you can create one or more of your own Application Interfaces. In either event, it is the Application Interface that is the object of the OPEN command, and it can be referred to with a full path file name.

The Procedure Catalog is associated with the Application Interface, so once a database is open, the user has access to all of the Procedures, Menus, Screens and Reports of that application.

All collections are cleared upon OPEN.

OPEN looks for the existence of a CONFIG file and does what it says during the process of opening. If they are not part of a CONFIG file, the following MODEs get reset to default values by OPEN. So if you want something other than the default for any of these, you should have them in a CONFIG file or insure that they get re-invoked after the OPEN. To re-invoke after the OPEN, a good place to put them is in the APPLICATION procedure. They are:

                                MODE STOP
                                MODE ESC
                                MODE RESTART


OPENing from the File Menu

When you compile DBD's and AI's, information about the location of these elements goes into a dictionary, the contents of which is used to produce a listpick of existing databases that is used when you OPEN a database from the File Menu. For example:

If you pull down the File Menu and select the first choice, "Open Data Base..." you will see something like this:

This is a list of all your current databases. (When you see this for the first time after installing Thunderbolt, there will be only one choice in it, and that choice will be EXAMPLE .)

The idea is that the user selects the database they wish to open and clicks OK. If the database you wish to open is not in this list, you can use the BROWSE to go find it and select it. After that it will be in the list.

When a database is OPENed in this manner (that is, opening from the File Menu rather than going directly to DCL with no database open and keying in the OPEN yourself) there is one other thing that happens. And that is that it automatically looks for a procedure named APPLICATION, and if it exists, executes it. If the procedure named APPLICATION does not exist, you see a diagnostic and control goes to DCL.

The APPLICATION procedure is used to accomplish any initializations and/or setup and then transfers control to the top-of-the-line Pull-down Menu from which the rest of the application springs.

So the user's experience is that he or she selects the database from the list and the next point of control is the application's Menu.

(You can make your application such that it is launched directly from the desktop, bypassing this File Menu step altogether. For more information about this, see "Procedures ." )


OPEN Options A, P and S

Cycle Errors: The four files that constitute the actual database are protected with cycle numbers that must agree when a database is OPENed. The reason for this is that if you ever restore a database from backup files you must restore the four files that match, you cannot pick some of them from one backup and the rest from another. Also, due to a power glitch or an OS glitch, the four files can get out of synch (fortunately, this latter is very infrequent, but it has happened to this author twice in the last 10 years).

If a cycle error happens, you are denied entry when you try to OPEN, and you get appropriate diagnostics. Here are your possible recovery procedures:

                If it was caused by a mix-up during file restoration procedures, do it
                again and get it right.

                You can recompile the DBD with an S option (Recreate Option) which
                saves the data space but reinitializes structure space, so you must
                rebuild indexes with a STRUCTURE command after the recompile.

                You can open with the A option (e.g., OPEN/A). This lets you get into
                the database (you are in a read-only mode with the A option) so you
                can UNLOAD all the data. Then you can delete and rebuild the database from scratch.

The P option OPEN allows you to open the Procedure Catalog only, not the database. You can then execute a procedure as long as that procedure only contains commands that do not require an open database (commands such as PROMPT, IF, CALC, SET, USERS, UNLOG, GOTO, etc.). This is ideal for an automated un-log procedure to use when you can not open a database because of max users. Also see MODE CHECKUNLOG .

The S option on OPEN says to open the database for exclusive use. You can't get in until there are no other users, but once you are in, no one else can open until you are through.

OPENing a Different Database from a Procedure

It is legitimate to execute a Procedure that contains an OPEN command. It could either be opening a different database altogether, or a different Interface (and therefore a different Catalog) to the current database.

When you do something like this, the next line (the first line after the OPEN command) must be a procedure call referring to a Procedure in the new Catalog, and that procedure call must have a Z option on it. The Z option tells us to clean up, accomplish the transition, and start at the top of the stack in the new catalog. For example, suppose this is a procedure in AAA:
                                                                                                                                                :
                                                                                                                                                :
                                                                                                                                OPEN BBB
                                                                                                                                APPLICATION/Z

Control transfers to the new Catalog (BBB) and the APPLICATION procedure in BBB is invoked. The Z option makes it all work. Control then stays in BBB, it does not come back to the next line of AAA. Of course, BBB could have been a full-path name.

Although this no longer has anything to do with OPEN, this seems like a good place to mention that there is also a way to execute a procedure in a foreign Catalog and have control return to the next line of the current procedure when it is done. "See Shared or Common Procedures ."