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Providing an Additional Level of Security: Creating an MDE
Access 2000 and above offer an additional level of security through the creation of an MDE file. An MDE (compiled database) file is a database file with all editable source code removed. This means that you eliminate all the source code behind the forms, reports, and modules contained in the database. An MDE file offers additional security because the forms, reports, and modules in an MDE file cannot be modified. Other benefits of an MDE file include a reduced size and optimized memory usage. To create an MDE file, follow these steps:
Before you dive into MDEs, it is important that you are aware of the restrictions they impose. If you plan ahead, these restrictions probably will not cause you too many problems. On the other hand, if you enter the world of MDEs unaware, they can cause you much grief. You should consider these restrictions:
- The design of the forms, reports, and modules in an MDE file cannot be viewed or modified. In fact, new forms, reports, and modules cannot be added to an MDE. It therefore is important to keep the original database when you create an MDE file. This is where you will make changes to existing forms, reports, and modules and add new forms, reports, and modules. When you are finished, you simply rebuild the MDE.
- Because you must rebuild the MDE every time you make changes to the application, the front-end/back-end approach is best when dealing with MDE files. This means that you store the tables in a standard Access database, and you store the other objects in the MDE file. You therefore can rebuild the MDE without worrying about the reconciliation of data.
- You cannot import or export forms, reports, or modules to or from an MDE.
- You cannot change code by using properties or methods of the Access or VBA object models because MDEs contain no editable code.
- You cannot change the database's VBA project name.
- You cannot convert an MDE to future versions of Access. You must convert the original database and then rebuild the MDE file with the new version.
- You cannot add or remove references to object libraries and databases from an MDE file. Also, you cannot change references to object libraries and databases.
- Every library database that an MDE references also must be an MDE. This means that if Database1 references Database2, which references Database3, all three databases must be stored as MDEs. You first must save Database3 as an MDE, reference it from Database2, and then save Database2 as an MDE. You then can reference Database2 from Database1, and finally save Database1 as an MDE.
- You cannot save a replicated database as an MDE. You must first remove the replication from the database. You accomplish this by removing the replication system tables and properties from the database. You can then save the database as an MDE and you can replicate the MDE and distribute it as a replica set. Any time you must make changes to the database, you must make them to the original database, resave the database as an MDE file, and then redistribute it as a new replica set.
- Any security that applies to a database will follow through to an MDE file created from it. To create an MDE from a database that you've already secured, you first must join the workgroup information file associated with the database. You must have Open/Run and Open Exclusive permissions to the database. You also must have Modify Design and Administer permissions to all tables in the database, or you must own all tables in the database. Finally, you must have Read Design permissions on all objects contained in the database.
- If you do not add error handling to code within an MDE, and an error occurs, no error message appears.
- If you want to remove security from the database, you must remove the security from the original database and rebuild the MDE.
As long as you are aware of the restrictions associated with MDEs, they can offer many benefits. In addition to the natural security they provide, the size and performance benefits MDEs offer are significant.TIPA great use for MDEs is for demo versions of your applications. Performance of MDEs is excellent, but more importantly, by using VBA code, MDEs can easily be rendered both time- and data-limited.
