How can I make my database more concise?
This is more of a comment, but since this is a lengthy response that's worth mentioning, I'm posting it as an answer.

Your database looks sufficient for your needs.  (Well, as best can be assumed from the diagram.)  I assume that the UserAccount table has a one-to-many relationship between the four tables Vehicle, Book, VideoGame and Movie (from here on, the V-B-V-M tables.)  Next, I assume that the Asset table has a one-to-one relationship with each link between the V-B-V-M table entries.  With this information, I would recommend moving the UserAccount_id from each V-B-V-M table, to the AssetTable.

Next, it seems that Asset is always associated with one of the four V-B-V-M tables.  Considering this type of setup, I would recommend creating an additional table-- AssetType.

+-----------+
| AssetType |
+-----------+
| id        |
| typeDesc  |
+-----------+


Next, update the Asset table and each V-B-V-M tables to include a AssetType_ID field.  the AssetType table should include one entry, for each type of asset.  In this case, Vehicle, Book, Video Game and Movie, each with a unique description and ID.

You may want to do this for a couple reasons-- First, you can now query the Asset table and discern what type of asset is stored in a specific record, without having to link the data to your four other V-B-V-M tables.  This will speed up your querying of the data, when all of the information from your four tables isn't needed.  Second, this also provides an easy means of linking in a textual description of the type of asset associated with the Asset entry. Again, without having to link to the V-B-V-M tables to figure that out.

Last, you may want to consider handling the barcode data differently.  If barcode is a simple look-up, you can add it to the asset table.  However, if barcode values have to be unique, keeping it in a secondary table is necessary because you'd have to put a constraint on the database.  You could do this if it was integrated in the Asset table, however, your vehicle data would cause problems because vehicles do not have barcodes.  To my knowledge most, if not all, major database engines won't allow you to define a unique field, that also allows null values because, then, the data is no longer unique.

You might be inclined to think that you could combine the Barcode field with the VIN.  Since VINs are unique and Barcodes are unique, and neither should be the same, why can't they be combined into one field on the Asset table, which allow you to drop the additional Barcode table.  I wouldn't recommend this because I think it gives the data less "focus".  

Yes, it is a form of unique object ID but barcodes are barcodes and VINs are VINs-- the concept behind both is completely different and consolidating the two can become confusing with time.  Furthermore, if you expand your project in the future, it could cause collisions.  Technically, I don't see a big problem with that (in your case) but I'd still highly recommend avoiding that option.

Also, I would also add the assetType_id to the Barcode table, for the same reasons you added it to the Asset table.