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Splitting a access database, or how to run ms-access in a multi-user mode.

By Albert D. Kallal
Friday, August 19, 2005

One of the neat things about ms-access is that you can take an application you written, and turn it into a multi-user application without having to change code.

Before we actually get into how to split a database and use ms-access in a muti-user mode, I want to clear up in your mind as to what this split idea is all about. Once this concept of a split database is clear in your mind, then the ďwhyĒ we split will become also clear.

 The first thing to realize when using access is that you are using a tool that creates software. This is a VERY important concept here. When you use other parts of office such as word, or Excel you are using an application that creates documents. So, with word, you have an application part called the word program (or so called executable).  After you LOAD the program called "word" you THEN can consume word documents. The same goes for Excel, you launch Excel, AND THEN open a document designed for that application. And, not to split hairs, but when you browse through a bunch of folders and then finally click on a word document you found, what actually occurs is the APPLICATION part loads first, and THEN the document part is consumed by the program part.

 The very simple, but important concept here is that software generally has two parts.

 

1 -  The program part, or software part

2 - The data part.

Some of you are wondering why the above simple and important concept needs to be pointed out? It turns out that a good number of systems administers and general users of computers have NOT thought about this common concept in software. It is not a hard concept to grasp that software has a data part + application part. In most organizations, installing the software on EACH desktop computer is not even given a second thought. So, if you want to use word, you install word on EACH computer. If you want to use Excel, then again, it is common knowledge, and common sense that you install the application on the workstation. Often, you will share some documents on a server, and allow users to open those documents. Note carefully how even in this case, the software (application part) is STILL INSTALLED on the workstation. Sure, you can put the DATA PART, or so called document part on a shared server folder. However, you STILL installed the software part on each computer.

So, for a typical network when you share data, you have one computer that is your server, and you share folders to computers on your network. 

In the above example, applications on each workstation can open their respective documents (data parts) that are placed on the server.

There are good many reasons as to why we install the software part on EACH workstation. A few reasons are:

I could add MANY more reasons to the above list, but suffice to say that it makes a lot of sense to install the software on each computer. I donít think there are too many people that have trouble understanding the above concepts.

However, when it comes to ms-access, the above concepts for some strange reason are complete ignored. Users all of a sudden get some type of freeze in the brain, and all of a sudden compete ignore how they deployed software on their computers for that last 15 years!

Ok, so what do applications and the data part that applications consume have to do with ms-access? It turns out that ms-access is MUCH more then just a data file. Ms-access is a software development tool. You might write a letter in word, but in ms-access in addition to typing in data, or text like word, you ALSO CREATE SOFTWARE. When you start using ms-access, then you have to put on a developers hat, and begin to think from a developer point of view.

You can use many different kinds of tools to create software with. These tools like c++, VB, and yes even ms-access are used to build forms (the user interface part), and also write code. These forms + code are what we call an application. It is this application part that you create that needs to be installed on each computer.  You always installed the word application on your computer. So, now that YOU ARE writing software, why should you throw out all of the ideas and concepts as to how software works on your computer? You can use a software tool like VB to create a word processing application, and once done, you will install that application on each computer. I should point out that you can also use ms-access to create a word processor, or a Pac man game. Make no mistake here; ms-access is a tool that allows you to create software. After you create that software, you need to install that software on EACH computer like you done with everything else you used.

The concept of splitting a database.

Ms-access is a most interesting software development tool. Access lets you build software, and ALSO keep the document part, or what we have been calling the data part in ONE FILE. This feature is really handy since you have ONE file that is both application part + data part. For a single user, this setup is very handy. Another nice feature of having data + application in one part is that you donít have to think about all the above software concepts when working on your application. I mean, one part is easier then two parts to deal with!!

 

This also why so many budding developers start out using ms-access, as it saves people having to think about the concept of a application part and a data part.  I do believe that most users can grasp the concept that Excel is an application, and that excel consumes a data part (a document part if you are thinking in terms of word, or excel). These same concepts must be applied when you create an ms-access application.

Further, the instant you go multi-user, then having two parts (data part + application part) becomes an advantage. The reasons are mostly the same as why all other applications on your computer split into two parts in the first place.

Ms-access has a splitter tool built in. From the main menu go;

Tools->database utilities->Database Splitter

After you run the splitter, the above application will become two files, or those so called two parts.

 

If you look at the above, the ONLY new concept you have here is linked tables. Everything else in your application will function as before. Splitting a database is thus easy, and requites little or no effort on your part. The only extra issue here to deal with is what we call linked tables. Now when you work with your application, all tables will be placed in the data only part. This data only file is commonly referred to as the back end (BE). If you add new fields to a table, modify the table designs, or add new tables, you MUST do all of this modifying and changing in the BE (data only file). You will NOT make table (structure) changes in the application part (FE). In fact, if you try to make a change to design of a table in the application part, you will find it is not possible! The application part is what is commonly referred to as the front end (FE).

What is now interesting about the above setup is you can make a copy of BOTH the FE, and the BE. You can even switch what BE the FE is connected to. This means you can test on test data, or test dangerous deleting code on a test BE. When you are happy that the test was ok, then you switch the connection back to the live, or production BE.

To switch, or manage the connection you use what is called the linked table manager in ms-access. You will no doubt become quite familiar with this linking process as you will now use the linked table manager to change what BE the FE connects to. Changing the connection will thus become part of your development routine, and is second nature to any experienced access developer.

The linked table manger in a2003 can be found via:

    Tools->database utilities -> Linked Table manager

Note that once you linked that FE to the BE, that link remains in effect. You can now copy the front end to a different location, but the linked connection will STILL continue to be pointing to that BE part. This means you have to use caution here. I worked on a copy of the FE, before working on this copy, I of course use the linked table manager to link the FE to a test copy of the BE. I am now able to test, delete, enter records and write new code etc. in this FE. This testing, and entering of test data etc. does not effect the users since their FE are linked to the production, or so called "live" BE. When I am done making changes to my FE, I can then re-deploy the FE to all the users on the network.

CAUTION CAUTION CAUTION! Note that before I deploy the new FE to each computer I MUST REMEMBER to re-connect the FE to the correct BE! I will admit that I have messed this process up once. The results are very nasty, as now all uses when they run the FE are connected to the WRONG BE. Any new data they enter will go into the test BE, and trying to sort this mess out and move new data from the test BE to the production BE is a nightmare. So, use caution here, and MAKE DOUBLE sure you connected the FE to the correct BE when you deploy.

One last thing about linking the FE to the BE is that you need to always use what is called UNC path names (Universal Naming Convention). All this really means is that you REALLY REALLY REALLY do not want to use mapped drive letters when you link. Besides, mapped letters are a 20 year throwback to the old PC DOS and CPM days when we used floppy disks! (When is the last time you used a floppy disk). Don't use mapped drives to a file share on the server. Drive mappings have all kinds of problems. Just plugging in a USB jump drive (memory stick) into your computer and the drive mappings can change. Further, you have to setup EACH pc for drive mappings and that is a pain. Further, even plugging in a digital camera can change drive letters. So, just avoid drive letters and mapping like the plague. Simply put, don't use them, and they are horrible from a support point of view. If you do risk using drive letters, then you will get a large increase in support calls for your software.

In other words, always use a path name to the back end files. What this means is when you use the linked table manger, always navigate through network places to the server, and then to the folder, and then the back end mdb file. DO NOT use mapped drives, and do NOT use the linked table manager to navigate to a back end by a drive letter.  If you use a mapped drive, then your path name will be something like: 

e:\mydata\backend.mdb

If you navigate by the network places, you will get a path name that does NOT have a drive letter. The path name (UNC) will look like

\\servername\mydata\backend.mdb

One last tip:

    Often after splitting some people find the performance is horrible! To restore the performance make sure that you FE in the startup opens up a table to the back end, and KEEPS it open. By keeping open a persistent connection, then the VERY slow connection process only occurs once.  If you don't want add code to the FE to open a table, you can create a small form in the FE that is attached to a table in the BE (you then minimize it, or even set it to invisible). Either way, you ALWAYS want to ensue that the FE has a connection to the BE in this fashion.

To be fair, this system of linked tables is little BIT more work. For example, now to add a table, you will have to open the BE, add your table. Close the BE. You now have to open the FE, and add a linked table to application that points to that new table. To add this linked table to the FE, you would go to the regular table tab where we always added a table. We then go new (for a new table), and select ---> link table (in place of design view). Since this is a few extra steps and hassle, often a developer will wait until a considerable amount of time has passed before splitting a database. It makes no sense if you don't have any users, and have not even deployed the application for multi-user mode to split.

Users often ask at what point in the development process do you split? Well, the answer is you just know!! At the start of the development process, you are creating tables left and right. And, further, at the start you have no users! After a considerable amount of time, that table creating process settles down to a dull roar. In fact, after a certain amount of time, if you are still adding tables to your application at a high rate, then something is wrong with the design. So, as you near the time when other users will start to use the application, then that is likely when you will split. And, hopefully by that time, adding new tables will now occur at a very much reduce rate. Thus the extra work of using linked tables will be of a minimal cost in terms of time and effort. Note that once you split, you don't as a rule un-split.

Compiling your application before you install on each pc.

At this point, you could deploy your FE to each workstation. However, you should not deploy something that users can change, mess with or modify to cause damage to your application, or worse the data! So, as a general rule, right before you deploy the application to your users, you compile the FE mdb into an mde file (the "e" stands for executable). This process of compiling removes all source code, strips out extra debugging stuff, and freezes the design of the mde. It is this mde that you should deploy to each workstation. That mde design can't be changed by your users. It is also the way developers deploy applications to clients, but those clients can't change the application.  When you create an mde, then the version of ms-access you have installed on the target pc in effect becomes your runtime support files. Note that VB, or even VB.net applications will not run on your pc unless you have the supporting runtime libraries installed. In our case, that means you need ms-access installed to make the mde (or any mdb for that matter) work on the target pc. While in most cases we assume that ms-access is already installed on the target pc, do note that you can also purchase a royalty free runtime system that allows you to package ms-access with your mde. This developerís edition of ms-access thus allows for deployment on computers that have not purchased a copy of ms-access. Regardless of the royalty free runtime edition, or regular edition of ms-access, you should create the mde for deployment. Both editions can create mde files, and thus you should give users an mde.

From the menu go;

Tools->database utilities->make mde file

(Note: that while versions of ms-access can often open, and use different versions of ms-access, to create an mde your mdb file MUST BE in the SAME version as access you are using. So, access 2003 can open, and work with a2000, and a2002 files, but to create an mde, you MUST use an mdb file of the SAME version of access that you are running. So, to create an mde in a2003, the mdb file must be also that version). This means you can't use access 2003 to create an mde for access 97 (however, access 2003 can create an access 97 mdb file...just not an mde one).

Even if issues of users changing the code, or you as developer don't care to protect your code, you REALLY still should deploy the mde. The mde is the end results of your application and is designed to be deployed to users. Further, this mde is smaller, runs faster, and is also more reliable (can't come un-compiled, or be modified by your users). To be fair, users can modify quires, but the forms, and code, and reports (the application) cannot be changed. Use caution when you make a mde, as you MUST keep the original mdb for further development (you cannot reverse this process!!). So, you deploy this mde to your users..and continue to work on the mdb. It probably don't need pointing out, but a mde that is not split is of little use, since you can't modify the forms, and if you deploy a un-split mde to your users, you will NOT be able to update the forms, reports, code etc. because you also have the data tables with the application part.

As a general rule, when you deploy the mde to each userís workstation, you will (or should) provide a shortcut on the desktop (and an entry in the start menu doesnít hurt either). Remember that part about you thinking like a developer here! I mean, how do you expect the user to launch your application? So, just like every other application, you should provide a shortcut on the desktop for ease of use to launch your application.

And, while we are at this, you do need to come up with a directory or location where you install this mde application on the userís workstation.

c:\program files\Your application dir\CustomersMailingList.mde

However, in many cases, some companies are now locking down their pc's very tight, and the program dir's are now often read only, and we need read/write for our mde file. So, the best location (at least for windows xp) is to use:

C:\Documents and Settings\All Users\Application Data

So, for our above application, I would likely use the following directory.

C:\Documents and Settings\All Users\Application Data\Custmailing\CustomersMailingList.mde

Of course, we don't want the user to have browse through all those directories just to launch the application (you don't do that to launch word etc, but provide a shortcut).

So, you need to create a shortcut on the desktop. Just right click on any blank area in desktop, and select new->shortcut. This process is easy.

The most common complaint about splitting is now you have to go around and install a new FE each time you make a change. The benefits of splitting far outweigh this ONE problem. And, the solution here is to either roll your own code to check for a new version and copy it from the server directory where the BE resides. That is what I do in my startup code, and it was only a few hours of work. A better and commercial grade solution is to grab Tony's free FE updater, this little gem simply updates your new FE to all users on the network when you place a new version in the directory where the BE is. It is a gem, and can be found here:

http://www.granite.ab.ca/access/autofe.htm

The above concepts will now allow you to safely work on the next great release of your software. Further, by adopting the standard way you installed all other programs on your computer, you also ensue a reliable operation.

Trying to work on an application and dance around users at the same time is like working on an airplane while it is in flight. It is really hard to imagine how anyone can develop an application that is un-split. Since users can't work while you modify an un-split application, then does everyone get to go home while you work? What happen when you make a simple coding mistake and then damage all of the production data? It is simply too dangerous to work on the actual code while users are running the application. Further, if you break something while users are working with your application, then those users likely will not want to use your software. Damaging user confidence can often result in people not wanting to use your software. Donít underestimate how user frustration can kill your project. If your users get discouraged, then often your project will fail. Remember, you now have to wear the developerís hat here!

So, split your application and develop in peace, and with peace of mind. Split your application so you don't drag it across the precious network. And, split your application so it runs reliably.

I also have a few notes AFTER my signature in this article that follow on using a security workgroup file, but you can ignore this info if you are not using a workgroup security file.

One last note:

Using a mdb file across a poor connection can damage (corrupt) a mdb file. I explain WHY a mdb file can corrupt in the following article, and also explain why you can't use a split database on a wireless network.

Click on this link to find out why a mdb file can corrupt, and about using ms-access on a WAN

 

 

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Albert D. Kallal
Edmonton, Alberta Canada
kallal@msn.com
http://www.members.shaw.ca/AlbertKallal

 

Specify options, and the security file in the shortcut.

While the linked table manager allows you to setup the connection (link) to the BE, you have no such luck when you are using a security workgroup file. So, if you are going to setup security, and have users/logons etc. for the database, then you need to place the workgroup file on the server. In these case, that security workgroup file should be placed in the SAME location (directory) as the BE resides. What this means is that your shortcut on the desktop needs to tell ms-access WHERE (more specially what) workgroup file to use. Unfortunately, to specify a workgroup file, your shortcut must now point to the msaccess.exe on your workstation, and the backend file, and the workgroup file! (You need to specify all 3 in that shortcut!). This file path will vary from version to version of ms-access. For access 2003 an example shortcut for the above mde file would thus be:

"C:\Program Files\Microsoft Office\OFFICE11\MSACCESS.EXE"

 "C:\Documents and Settings\All Users\Application Data\Custmailing\CustomersMailingList.mde"

 /wrkgrp "\\servername\shardFolder\custordata\mailing.mdw"

Of course, the above goes all on one line. In the shortcut properties 'target' (each part is separated by a space). Note that you could deploy the workgroup file to each workstation also, but then that would not allow you to add new users, or change passwords without re-deploying this data file. And, since the workgroup file is just a data file, then it should be shared to all users, and the sensible place is thus the same location as the BE.

During development, I get so tired to typing in the password, that I often make a shortcut on my computer that supplies the admin user and the password so I don't have to type it each time. So, add to the above shortcut:

 /User "Admin" /pwd "mypassword"

The above also lets me work on different projects during the day, and each shortcut thus selects the workgroup file. And, for the many regular mdb files that don't have security, then no prompts occur since using a shortcut means I do NOT have to join a workgroup file.

Of course, all this setup stuff really means that you should start setting up some install scripts, and that means you want to consider using some install tools.  That is a whole another topic, and another future article!

 

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