Working with historical versions
To examine archived information, you must access the data through a historical version. When connecting to a historical version, you are connecting to a defined moment in time. The moment is either the current database's time (the DEFAULT historical marker), a predefined historical marker, or a database date and time you specify.
What date and time is it?
When working with archived information, it is important to understand that the date and time recorded in the gdb_from_date and the gdb_to_date fields of the archive class reflect the date and time a transaction took place—when a feature was added, edited, or removed from the feature class. This date and time is received from the server OS. This affects how you access and query the archive class.
If you are working in a time zone different than the server, queries against a moment in time must reflect the server's time, not the time on the client OS. For example, if you perform an edit at 9:05 a.m. (PST) but the DBMS resides in New York, the transaction time recorded for this edit is actually 12:05 p.m. (EST). Subsequently, if you were to query the historical version for 9:05 a.m., you would no longer see the edit, because at 9:05 a.m. on the server, that feature had not been created. To see the newly added feature, you would need to query the DBMS for 12:05 p.m.
If you specify a date and time prior to the moment that archiving was enabled, no data will be accessible. Archived data is only accessible from the moment you enable archiving forward. For example, if you enable archiving on 2/1/10, then change to a historical version specifying the date 1/31/10, no data will appear.
The Refresh Database Time button is available in most of the dialog boxes that let you define a historical version. Clicking this button updates the date control with the current database time. This ensures that the date and time are consistent between the client and the database server.
The DEFAULT historical marker
Connecting to the DEFAULT historical marker displays the current representation of the archive classes, which is equivalent to the class representations in the transactional DEFAULT version.
Connecting through the DEFAULT historical marker allows a read-only connection, which can actually consume fewer database resources than working with the equivalent versioned class. The archive class does not rely on the information stored in the delta tables or the ArcSDE repository versioning tables, meaning that querying the archive class for all records that are currently active (gdb_to_date of 12/31/9999) can often be faster than querying the DEFAULT transactional version.
Connecting to a different historical version
To connect to a date and time other than that represented by the DEFAULT historical marker, you can define a historical marker, which is a named moment used to quickly connect to important dates and times, then choose to connect to that, or type a date and time. See the topic on historical markers to learn how and when to create historical markers.
There are two different ways to connect to a historical version in ArcGIS for Desktop: using either the Geodatabase Connection Properties or Change Version dialog box.
Connecting to a historical version from the Geodatabase Connection Properties dialog box
The Geodatabase Connection Properties dialog box lets you specify to which version of the geodatabase you will connect. To open it, right-click a database connection in the Catalog tree in ArcCatalog or ArcMap and click Geodatabase Connection Properties.
First, choose Historical version. Then you have the option to pick from a list of historical markers or a specific date and time.
As mentioned previously, you can click the Refresh Database Time button to populate the specific date and time field with the current database time. Alternatively, you can use the pull-down calendar to choose a date from the calendar, or type a date and time directly in the field.
After you change versions, the data you preview from this connection file in ArcCatalog or view in ArcMap is the archive-enabled data to which you have access for the historical version referencing the moment you have selected.
Connecting to a historical version from the Change Version dialog box
To open the Change Version dialog box, do one of the following:
- Right-click the database in the ArcMap table of contents and click Change Version.
- Click the Change Version button on the Versioning toolbar in ArcMap.
When the dialog box opens, click the Historical tab at the bottom.
You can choose from a list of historical markers or choose or type a specific date and time.
After you connect to a different historical version, ArcMap displays the data for the historical version referencing the moment you have selected.