The given class of attacks (Denial of Service/DoS) aimed to violate the access to web-server. Usually, the attacks, which are directed on denial of service, are released on the network level, but they also can be directed on an application level. When the hacker uses web-application functions, he can exhaust critical system resources, such as computational performance, core memory, drive space or communication bandwidth. If any of the resources will reach its maximum of loading, the entire application will be unavailable.
Attacks may be directed to any of the components of the web-application, such as a DBMS server, authentication server, etc.