One of the most common features I have seen in common use for SharePoint (prior to 2010) in Intranet environments for Team site is Calendar’s. Not only the Calendar list type, but also the ability to add a Calendar view to any list that has the desired columns to construct a Calendar – such as Start, End, Title etc. While this was all great for a single site/calendar, the problem of having to track numerous calendar’s remained. With introduction of Outlook 2007 bi-directional integration with SharePoint, and particularly the ability of Outlook to overlay calendar helped bridge the gap. Now one could connect to number of team sites, and setup Calendar overlays in Outlook using varying colours, to easily identify event source and yet benefit from the plotting of events on single Calendar view. This was all good, but each user in your Enterprise was supposed to setup in a “pull” fashion. This is good for flexibility, not so good when you need to “push” consistency and productivity (re-use). So, what was missing on SharePoint is the ability to have server-side overlay’s that everyone can see – in a single place, aggregating multiple sources. Until SharePoint 2010 arrived! Calendars Overlay in SharePoint 2010 There are Calendar lists and Calendar views. View can be created for almost all lists, as far as you have desired column’s in a list like Start, End, Title etc. to be able to describe and plot an item in a Calendar format. In SharePoint 2010, create a new Calendar list. Go to Calendar ribbon tab, and click Calendar Overlay. You get the screen with list of existing Overlay’s associated with current Calendar (list – in our case). Click on “New Calendar”… Notice the breadcrumb! You are adding Overlay to existing list (Team Calendar – in our case). You have choice of “pulling” Calendar info from an existing Calendar (list/view) in SharePoint or even from Exchange! Set standard info like a name, description and decide the colour you want for the items in aggregated Calendar overlay. Select the source site/list/view, anywhere in farm. When you select Exchange as source of Calendar, you get option to add OWA and Exchange Web Service url. I will cover details of connecting with Exchange in another post, and focus on Overlay’s with SharePoint for this one. Once you have added a new Calendar overlay to existing Calendar veiw, you get something like below for Day view, Week view, and Month view respectively Notice the Overlay colours: Now, if you decide to connect this Calendar to Outlook to sync the items, it will only sync items from main view, and not from Overlay source. So such Overlay of calendar’s is server-side aggregation only. That increases my curiosity, so I try adding the Calendar list view as a web-part on a new page. As you see, this instance of view didn’t include item from source that we had added to default Calendar view. This is – probably – due to the fact that this is a new web-part view for the page. If you want to add overlay to this one, you have to redo that from Ribbon. This also means, subject to purpose and context you get the flexibility to decide what overlay is suited. Also you can only add 10 Overlay’s to an existing view instance. Conclusion Calendar Overlay is clearly a very useful feature that fills a gap of not being able to aggregate information from multiple sources into a Calendar view within context of current items. Source of items can be existing SharePoint calendar views on any site, or even Exchange (via OWA/Exchange web services). List type for source doesn’t matter, it just need a Calendar view type available. You can have 10 overlays. Overlays are for the specific view only, and are server-side only – which means they do not get synced in Outlook. While you can drag-drop current list items, you cannot edit overlay items as they are read-only within scope of current Calendar view. You can of course click on source Overlay item to edit at the source. I’d like to hear, how you think Overlay’s will help you in your case, or how you are already using them... Enjoy SharePoint! --Sharad
