In view of present scattered and incompact research of the field in mainland, while systemic and meticulous research is also necessary for the development of legislation and economy demands, during the course of property legislation and asset securitization, I choose the issue of the accessory character and independent character of mortgage as the subject of my thesis.

The lodging contract,the hotel agent holds the obligation of offer and attached duty.

Traced to German Case Law,the theory of collateral obligation comes to develop with the establishment of good faith principle.

The set of self-service deposit in supermarkets is not based on the collateral obligation of contract of sale,but the contract between consumers and supermarkets.

In order to improve the market,law stipulates the party with more imformation the collateral obligation.

The paper studies the characters of contingent diffusion products,and constructs a contingent diffusion model for them based on the bass modcl,and then takes the wireless Internet subscribers for example to build the contingent diffusion model,and forecasts the tendency for future.