Notification content types

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Current chapter: Creating HDML Services that "Push" Information
Section 33 out of 67 total sections , Section 2 out of 11 sections in this chapter

Notification content types

An HDML service can send notifications containing one or more of the following entities:

Alert--a command that instructs the UP.Phone to beep or display a visual signal to notify the subscriber that new information is available.
Cache operation--a command that removes an individual URL, or all the URLs for a service, from the UP.Phone cache.
HDML decks
Images
Digests

Decks, images, and digests are described in Valid content types. The sections below describe the alert and cache operation content types in more detail.

Alerts

From the user's perspective, the most obvious notification content type is an alert. An alert typically includes a very short message (or title) and a URL that the user can request.

When an HDML service sends an alert, the UP.Phone can do any of the following:

Beep, buzz, or flash a light, indicating that the alert has arrived (these features are not available on all UP.Phone models).
Display a popup message card (shown in Figure 5-1), which informs users that an alert has arrived and allows them to view the alert or skip it.
Display an alert icon (as shown in Figure 5-2)

The user can configure the UP.Phone to enable or disable each of these alert indications.

FIGURE 5-1. Popup alert message from the UP.Mail service

In addition to providing the alert indications described above, the UP.Phone adds each alert it receives to its Inbox card. The Inbox card is normally accessible from the user's Home Menu (as shown in Figure 5-2).

Users can navigate to the Inbox card at any time to view the alerts they have received most recently. When the user chooses the alert in the Inbox, the UP.Phone requests the URL provided by the alert.

FIGURE 5-2. UP.Phone Inbox card displaying UP.Mail and UP.Market alerts

NOTE Most devices running the 3.1 UP.Browser reserve approximately 1500 bytes for storing nine alert titles and associated URLs in the Inbox. As a result, you should limit your alert information (title and URL) to a combined size of 160 bytes. You should also keep your alert title as short as possible so users can read it without scrolling.

Cache operations

UP.Phone caching can greatly improve the performance perceived by the user. When a user visits a URL, the UP.Phone caches it. The next time the user requests the URL, the UP.Phone retrieves it directly from its cache instead of re-requesting it from the UP.Link server. This feature is described in Improving performance by modifying phone caching.

Although the TTL option allows you to specify when a UP.Phone expires a URL from the cache, sometimes you might want to explicitly remove a URL from the cache--for example, if it becomes obsolete before its TTL expires. To remove a URL from the cache, you use a cache operation. A cache operation can instruct the UP.Phone to remove either individual URLs or all the URLs for the current service from its cache.

You can include a cache operation in a digest along with HDML content (as described in Modifying UP.Phone caching). However, in some cases, you might not want to wait for the user to request a digest to remove a URL from the cache. Instead, you might want to simply remove the URL asynchronously "behind the scenes". To do this, you send a notification containing a cache operation.