Executable Web element

An executable web element is a leaf in the tree of web elements that will be generated as an executable entity. It can be a dynamic HTML web file, a zone or a polymorphic zone. In the presentation and navigation model, the web elements are linked together via decision centers. A dynamic page can be an entry web file that is composed of a number of web file fragments via composer decision centers. A web file fragment is an ordinary HTML text file whose only contents between two precise tags (typically body) are taken into account. To model the navigation, non fragment HTML web files are linked together via linker decision centers with business rules which express constraints.

Entry context

Every executable web element has a (possibly empty) entry context that provides the environment in which the dynamic page is executed. The entry context consists of :

• session variables
• web element variables

Session variables

Session variables are variables accessible implicitly in every web element of the site. A session variable can be either persistent (stored in the database)

or transmitted in the URL from page to page.

When at least one persistent session variable is defined, the object session itself is accessible under the name session and the type OclObject in case when it is necessary to obtain the Object Identifier of the session object. To know the oid of the current session is necessary when one passes for example from the protected part of a site towards the non protected part of a site. See paragraph about Session management.

The default value expression of a session variable is evaluated when the session object is created. If a session variable has no default value, the default value for its type is assigned to the variable. See paragraph about Xion data types. No other entry variable is accessible in the expression that gives the default value for persistent session variables. Persistent session variables values are accessible in the default expression of transmitted session variables.

If the type of a persistent session variable is a class, the object that represents this variable can be linked to the session object via an association or a composition.

If linked with an association, the object is not deleted when the session expires.

If linked with a composition, the object is deleted when the session expires.

Web element variables

Web element variables are variables accessible in the web element in which they are defined.

Web element variables with no default value must be explicitly assigned when the web element is embedded in an other one or when the web element is the target of a link. If the parameter corresponding to this variable is not defined in the calling URL, the default value for the type of the variable is assigned to it.

Web element variables with default value expression can be ignored when the web element is embedded in an other one or when the web element is a target of a link. If the parameter corresponding to this variable is not defined in the calling URL, the expression giving the default value is evaluated and its result assigned to the variable. Session variables are accessible in the expression giving the default value.

If the type of a web element variable is a class, the life cycle of the object that represents this variable is not handled by Netsilon. The designer of the site must determine when such an object should be created and deleted.

Private web element variables are not visible from outside the web element and not passed in the URL. They must have a default value or be initialized in the entry action and are visible in the expressions present in the element.

Entry action

Almost every executable web element has a (possibly empty) entry action. Entry actions are written in Xion and are executed after the entry context has been elaborated and before any output is sent. Entry actions have access to the variables in the entry context and to the business model. Modifications made to an entry variable in the entry action are seen in all the decision centers embedded in this web element. Variables defined in the entry action are only visible in it.