Modifying Information Offline
Adam Bosworth continues his description of how to build a web services browser in an intermittently connected world:
this new browser I’m imagining doesn’t navigate across pages found on the server addressed by URL’s. It navigates across cached data retrieved from Web Services. It separates the presentation – which consists of an XML document made up of a set of XHTML templates and metadata and signed script – from the content which is XML. You subscribe to a URL which points to the presentation. This causes the XML presentation document to be brought down, the UI to be rendered, and it starts the process of requesting data from the web services. As this data is fetched, it will be cached on the client. This fetching of the data normally will run in the background just as mail and calendar on the Blackberry fetch the latest changes to my mail and calendar in the background. The data the user initially sees will be the cached data. Other more recent or complete information, as it comes in from the Internet, will dynamically “refresh” the running page or, if the page is no longer visible, will refresh the cache.
I recommend that the model is that, in general, data isn’t directly modified. Instead, requests to modify it (or requests for a service) are created. For example, if you want to book a restaurant, create a booking request. If you want to remove a patient from a clinical trial, create a request to do so. If you want to approve an expense report, create a request to approve it. Then relate these requests to the item that they would modify (or create) and show, in some iconographical manner, one of 4 statuses:
1) A request has been made to alter the data but it hasn’t even been sent to the internet.
2) A request has been sent to the Internet, but no reply has come back yet.
3) The request has been approved
4) The request has been denied.
the important thing is that it works really well even when the connection is poor because all changes respond immediately by adding requests, thus letting the user continue working, browsing, or inspecting other related data. By turning all requests to alter data into data packets with the request, the user interface can also decide whether to show these overtly (as special outboxes for example or a unified outbox) or just to show them implicitly by showing that the altered data isn’t yet “final” or even not to alter any local data at all until the requests are approved.