1. A system for providing a mobile device application with access to a network resource via a native shell, the system comprising: a network resource access software development kit for use on a mobile application development station, said network resource access software development kit including a network resource tag library, said network resource tag library comprising a plurality of textual tags that serve as references to respective network resources, including network resources that have different respective application programming interfaces (APIs), said plurality of textual tags adapted to be incorporated into markup language of mobile device applications to enable the mobile device applications to access corresponding network resources over a network; a network application system comprising a computing device, said network application system configured to receive, from one or more mobile application development stations, mobile device applications having markup language content that includes tag-based references comprising tags selected from the tag library, said tag-based references referencing particular network resources; and a native shell service that runs on a mobile device, wherein the native shell service is configured to run mobile device applications, wherein said native shell service is configured to identify, in markup language content of a mobile device application, a tag-based reference to a network resource that has an API for accessing the network resource, and wherein the native shell service is configured to use a network resource resolution service that is external to the mobile device to enable the mobile device application to access the referenced network resource via the API without the mobile device application specifying said API.