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Does Access contain metadata?

Discussion in 'Information Technology' started by Techno, Jul 28, 2006.

  1. Techno

    Techno
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    Guest

    If Access contains metadata, is it possible that information deleted from an
    Access database could be recovered? If so, how hard is it to do this?
     
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  3. '69 Camaro

    '69 Camaro
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    Guest

    Hi.

    > If Access contains metadata, is it possible that information
    > deleted from an Access database could be recovered?


    An Access database file contains some metadata, but it's not as extensive as
    you'll find in client/server databases. Recovery of deleted information from
    an Access database is severely limited. It's usually best, and cheapest, to
    restore from a recent backup when these types of boo-boos are made.

    > If so, how hard is it to do this?


    It depends upon what was deleted. If you deleted an object in the Database
    Window, then select the tab for that type of object and press <CTRL><Z> to
    "undo" the operation. If that was the most recent operation in that tab, it
    will "undo" the object's deletion, but only for one object, so if you deleted
    more than one object, you are probably SOL.

    If you deleted one or more tables and you haven't closed the database since
    they were deleted, and you haven't compacted the database, and the tables
    were deleted in the GUI (not by using SQL, VBA code or a macro), then please
    see the following Web page for a way to recover them:

    http://support.microsoft.com/kb/209874

    If you deleted records, then they've been "marked for deletion" by Jet, so
    Jet overwrites parts of these records while doing its housekeeping, which
    makes these records mostly corrupted data. Because of this, recovery
    services can recover as much as 5% of deleted records, so it's usually not
    worth the expense. It's best to restore from a recent backup. You _do_ have
    a recent backup, don't you?

    HTH.
    Gunny

    See http://www.QBuilt.com for all your database needs.
    See http://www.Access.QBuilt.com for Microsoft Access tips and tutorials.
    http://www.Access.QBuilt.com/html/expert_contributors2.html for contact info.


    "Techno" wrote:

    > If Access contains metadata, is it possible that information deleted from an
    > Access database could be recovered? If so, how hard is it to do this?
     
  4. Techno

    Techno
    Expand Collapse
    Guest

    Thanks for the response. I was actually asking the question about recovering
    data from a security standpoint. I want to ensure that certain information in
    an Access file cannot be recovered when the file is given to an outside
    party.

    Let's say a copy is made of an Access file which is later redacted to remove
    information in column B (for example) before being turned over to another
    party. Would this COMPLETELY remove the data? The data in question in highly
    sensitive and must not be recoverable by an outside party.

    Thanks,

    Techno

    "'69 Camaro" wrote:

    > Hi.
    >
    > > If Access contains metadata, is it possible that information
    > > deleted from an Access database could be recovered?

    >
    > An Access database file contains some metadata, but it's not as extensive as
    > you'll find in client/server databases. Recovery of deleted information from
    > an Access database is severely limited. It's usually best, and cheapest, to
    > restore from a recent backup when these types of boo-boos are made.
    >
    > > If so, how hard is it to do this?

    >
    > It depends upon what was deleted. If you deleted an object in the Database
    > Window, then select the tab for that type of object and press <CTRL><Z> to
    > "undo" the operation. If that was the most recent operation in that tab, it
    > will "undo" the object's deletion, but only for one object, so if you deleted
    > more than one object, you are probably SOL.
    >
    > If you deleted one or more tables and you haven't closed the database since
    > they were deleted, and you haven't compacted the database, and the tables
    > were deleted in the GUI (not by using SQL, VBA code or a macro), then please
    > see the following Web page for a way to recover them:
    >
    > http://support.microsoft.com/kb/209874
    >
    > If you deleted records, then they've been "marked for deletion" by Jet, so
    > Jet overwrites parts of these records while doing its housekeeping, which
    > makes these records mostly corrupted data. Because of this, recovery
    > services can recover as much as 5% of deleted records, so it's usually not
    > worth the expense. It's best to restore from a recent backup. You _do_ have
    > a recent backup, don't you?
    >
    > HTH.
    > Gunny
    >
    > See http://www.QBuilt.com for all your database needs.
    > See http://www.Access.QBuilt.com for Microsoft Access tips and tutorials.
    > http://www.Access.QBuilt.com/html/expert_contributors2.html for contact info.
    >
    >
    > "Techno" wrote:
    >
    > > If Access contains metadata, is it possible that information deleted from an
    > > Access database could be recovered? If so, how hard is it to do this?
     
  5. John Vinson

    John Vinson
    Expand Collapse
    Guest

    On Mon, 19 Jun 2006 08:33:02 -0700, Techno
    <Techno@discussions.microsoft.com> wrote:

    >Let's say a copy is made of an Access file which is later redacted to remove
    >information in column B (for example) before being turned over to another
    >party. Would this COMPLETELY remove the data? The data in question in highly
    >sensitive and must not be recoverable by an outside party.


    I would not count on it, and - as much as I love working with Access
    - I'd be very cautious about using Access for such sensitive data in
    the first place.

    Compacting the database will recover the space, but it is not designed
    to seek out and specifically overwrite all such data. A binary sniffer
    (either on the .mdb file or on the hard disk where it was stored
    before being compacted) could very likely extract information that has
    been nominally "deleted".

    John W. Vinson[MVP]
     
  6. '69 Camaro

    '69 Camaro
    Expand Collapse
    Guest

    Hi.

    > The data in question in highly
    > sensitive and must not be recoverable by an outside party.


    If you need to safeguard the data, then don't store it in Access. Store it
    in a client/server database, such as SQL Server or Oracle. Both Microsoft
    and Oracle offer free versions of their latest client/server databases, SQL
    Server 2005 Express and Oracle 10g Express, respectively, so you wouldn't
    even have to worry about the added expense of licensing.

    > Let's say a copy is made of an Access file which is later redacted to remove
    > information in column B (for example) before being turned over to another
    > party. Would this COMPLETELY remove the data?


    No. It wouldn't. Say you delete the AnnualSalary column from the table,
    because you don't want the outside party to know how much they'd have to
    offer to draw your best employees away from your company. If you open the
    table afterwards, you'd see that there is no longer an AnnualSalary column,
    so all of the data in that column appears to be gone. However, Jet never
    deletes columns from a table. All new records will store a NULL value for
    this column but the previous records will still contain the data that was in
    the AnnualSalary column at the time of deletion. This data can be read with
    a Hex editor. Even if you compact the database, the data still remains in
    the deleted column of this table.

    Say you ran an UPDATE query on the AnnualSalary column to set all values to
    NULL. If you open the table afterwards, you'd see that there are no longer
    any values in the AnnualSalary column. However, the file may contain this
    deleted data, anyway, which can be read with a Hex editor. Any records which
    have previously been deleted are only "marked for deletion," so they aren't
    actually zeroed out. These previously "deleted" records, if not already
    overwritten, would still contain values in the AnnualSalary column after the
    UPDATE query sets the rest of the visible records to NULL. In addition, if
    there's an index on this field, then the index's data leaf pages could
    contain these values, albeit the corresponding index records would also be
    marked for deletion.

    Once the database is compacted, the records will be reordered so that they
    occupy contiguous space within each data page, and the records that had been
    marked for deletion will not be carried over to the new file, but it's
    possible to find the rows for these "deleted" records inside the "slack
    space" that each data page contains in the new file with a Hex editor.
    (Note: From testing, it's not clear whether or not these "deleted" records
    were from a previous compaction that the new file is overwriting.) If these
    "deleted" records are in the slack space, then they'll remain there until Jet
    eventually overwrites them with new records. Same thing with the index
    records.

    The bottom line is that you can't guarantee that at least some of the data
    won't remain in the file after it appears that you've successfully removed it.

    HTH.
    Gunny

    See http://www.QBuilt.com for all your database needs.
    See http://www.Access.QBuilt.com for Microsoft Access tips and tutorials.
    http://www.Access.QBuilt.com/html/expert_contributors2.html for contact info.


    "Techno" wrote:

    > Thanks for the response. I was actually asking the question about recovering
    > data from a security standpoint. I want to ensure that certain information in
    > an Access file cannot be recovered when the file is given to an outside
    > party.
    >
    > Let's say a copy is made of an Access file which is later redacted to remove
    > information in column B (for example) before being turned over to another
    > party. Would this COMPLETELY remove the data? The data in question in highly
    > sensitive and must not be recoverable by an outside party.
    >
    > Thanks,
    >
    > Techno
    >
    > "'69 Camaro" wrote:
    >
    > > Hi.
    > >
    > > > If Access contains metadata, is it possible that information
    > > > deleted from an Access database could be recovered?

    > >
    > > An Access database file contains some metadata, but it's not as extensive as
    > > you'll find in client/server databases. Recovery of deleted information from
    > > an Access database is severely limited. It's usually best, and cheapest, to
    > > restore from a recent backup when these types of boo-boos are made.
    > >
    > > > If so, how hard is it to do this?

    > >
    > > It depends upon what was deleted. If you deleted an object in the Database
    > > Window, then select the tab for that type of object and press <CTRL><Z> to
    > > "undo" the operation. If that was the most recent operation in that tab, it
    > > will "undo" the object's deletion, but only for one object, so if you deleted
    > > more than one object, you are probably SOL.
    > >
    > > If you deleted one or more tables and you haven't closed the database since
    > > they were deleted, and you haven't compacted the database, and the tables
    > > were deleted in the GUI (not by using SQL, VBA code or a macro), then please
    > > see the following Web page for a way to recover them:
    > >
    > > http://support.microsoft.com/kb/209874
    > >
    > > If you deleted records, then they've been "marked for deletion" by Jet, so
    > > Jet overwrites parts of these records while doing its housekeeping, which
    > > makes these records mostly corrupted data. Because of this, recovery
    > > services can recover as much as 5% of deleted records, so it's usually not
    > > worth the expense. It's best to restore from a recent backup. You _do_ have
    > > a recent backup, don't you?
    > >
    > > HTH.
    > > Gunny
    > >
    > > See http://www.QBuilt.com for all your database needs.
    > > See http://www.Access.QBuilt.com for Microsoft Access tips and tutorials.
    > > http://www.Access.QBuilt.com/html/expert_contributors2.html for contact info.
    > >
    > >
    > > "Techno" wrote:
    > >
    > > > If Access contains metadata, is it possible that information deleted from an
    > > > Access database could be recovered? If so, how hard is it to do this?
     

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