A web-based application constructor can be used to construct a web display. A specification, for constructing a web display to contain page components that display data from heterogeneous data sources, may be created. The page components may be associated with uniform resource locators. Data from heterogeneous data sources may be retrieved to produce the web display. Display and update of the page components may be controlled using the uniform resource locators. User-selectable options may allow annotation of the page components for a page with comments.