PPML - Resource Management

Resource Management

Reuse of resources solves only part of the problem. Ensuring that all the required resources are available on the printer is another big problem. In PPML this problem is solved by allowing references to resources via URL's (Universal Resource Locator). Now the printer can retrieve the resource via the URL if it doesn't have that particular resource yet. This eliminates the need to send all the needed resources along with the print job. The printer will simply retrieve those resources that it needs on the fly. If it already has the resource in its cache it does need not retrieve the resource. This works in the same way as a browser that gains speed by loading (parts of) a webpage from its cache.

Not including resources in a print job leads to the potential problem of version control. PPML solves this problem by allowing the producer of the print job to specify a checksum for each resource that is referenced. A checksum is a large number that is calculated from the contents of a resource. By comparing a given checksum against the checksum of the resource in the cache the printer can check that it has the correct version of the resource.