an enforceable security interest. In certain cases, the possession does not need to be actual possession, but may be constructive possession. For example, possession of a document of title will often suffice where it is not possible to possess the goods. In many legal systems, there may also be constructive possession by attornment. The law relating to perfection of security interests by taking of possession can sometimes be confused with the law relating to the granting of security interests, which provides that the deposit of certain assets (usually documents of title) can amount to an equitable mortgage of the goods. Registration or filing Certain security interests may be perfected by some kind of registration or filing. Although the terms are used interchangeably, it is more accurate to speak of registration as the lodgment of particulars, and filing as the lodgment of the security instrument itself. Generally systems of registration divide into two types: registration against a particular debtor; and registration against a particular asset. Each has its own advantages and disadvantages. Registration against a particular asset only tends to be practical where the assets are of a nature and substance that makes it feasible to have a register for recording security interests against them. Most countries have systems for the registration of security relating to land, aircraft, ships and intellectual property rights. The advantage of a register relating to the asset is that if the debtor wishes to provide an asset as collateral, the proposed lender can swiftly check definitively whether the asset is encumbered or not. Issues arise when a secured creditor does not file with the correct office, leaving potential lenders without notice of encumbrances on potential collateral. One particular note regarding the perfection of security interests in a patent is an illustration of this issue of miscommunication. In order to perfect a security interest in a patent, it is not enough that you file a patent with the Patent and Trademark Office. A secured creditor, in order to perfect its interest, must file in the UCC Filing system. This is because the Patent act does not "preempt" the state requirements for filing. In other contexts, filing outside of the UCC filing system is appropriate to perfect a security interest. Specialist registers in some jurisdictions cannot always be considered "a one-stop source of information". Registration against a debtor tends to operate by way of requiring the registration of