Data Pages
 

A data page (formerly "declare pages") rule defines the contents of a clipboard page. There are two types:

• Read-only — provides a read-only page available to only one Thread, to a Requestor, or to multiple requestors (on one Node) in your application. For example, a page can contain daily prices for a set of commodities, bonds, or currencies, an organization chart, or quantity-on-hand inventory data extracted hourly (rather than in real time on-demand) from an external system. These pages can be "global", available to all requestors on a node.

Read-only data pages can be modified only during page load and post-activity processing. Read-only data pages appear in the Data Page list on the clipboard.

• Editable — provides the initial contents of a page that, thereafter, can be accessed in normal read-write mode. Editable data pages appear in the User Page list on the clipboard. Editable data pages do not have a refresh strategy and cannot be node-level in scope.

Data pages load synchronously by default. To have them load asynchronously, so users can take action on a work item while other content is still being loaded, do one of the following:

• Select the Defer load check box on a section whose source is a data page.
• Use the Load-DataPage step method in an activity. Wait for the data page to load by using the step method Connect-Wait. (In between these two steps you can include steps to do other processing that does not depend on the data page being loaded.)

Benefits

Data pages can improve performance and reduce memory requirements when all or many requestors in an application need to access information.

For example, a data page may hold last night's closing U.S. stock prices in a Value Group property indexed by ticker symbol, so that the property reference D_Stock.Price("IBM") is the closing price for IBM shares. The first time each evening (after the 4:30 P.M. New York market close) that a requestor attempts to access the page, the system automatically loads the page with the latest end-of-day prices. The page can remain unmodified in memory until the next day's closing.

Even more significantly, you can reference data pages using parameters, and the data page can create on the clipboard unique instances of itself for each unique reference, with data related to the parameter values. For instance, a single data page, D_Customer, can create many instances of itself on the clipboard as your application requires, and each instance has exactly and only the information about that particular customer.

In other situations, data values are not static but may change infrequently; the system automatically checks the data page contents (using a when condition rule) before each property access to see whether a fresh recomputation is needed. For example, a page may list the part numbers or SKU numbers of items that are out-of-stock, extracted from an inventory control system. Recomputation is needed only as often as an out-of-stock condition begins or ends, not each time the inventory changes.

Where referenced

Many rule types can reference the pages created by data pages rules, and provide values for the properties on such pages; they do not explicitly reference the rule.

To locate, review, and manage data pages:

• Open the Data Explorer in the Explorers tab, select a data type and expand its display, and click one of its data pages to display it.

• Click > Data Model > Clipboard Pages > Data Pages to list data pages used by the current application. See Data Model category — Clipboard Pages page.

When a requestor accesses a data page, the data page creates a new instance of itself on the clipboard. Each data page, and each instance of it on the clipboard, has a name that starts with Declare_ or D_. Rules of any type that can reference properties on pages other than the current or primary page — including activities, decisions , and parse rules — can reference properties on data pages in a read-only or "right-hand" context. Typically, the rule form identifies the name and class of a data page on the Pages & Classes tab.

Access

Use the Data Explorer to list all the Data Pages available to your application.

Category

Data Pages are instances of the Rule-Declare-Pages class. They are part of the Data Model category.

Notes

Data pages are not created at system startup; they are created only when first accessed.

Ordinarily, data pages do not persist; they are not saved to the PegaRULES database but are reconstructed when next accessed and the previous version is expired.

On the Clipboard tool display, data pages appear as a group named Data Pages.

On the Performance tool full details display, you can review (for your own requestor session) elapsed time and CPU time statistics associated with creating, finding, and accessing data pages, and counts of the number of node-level data pages your requestor has accessed.

The system maintains node-level data pages in a cache.

Related information

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