The 5 Classes of Revit Elements

Classification of categories of elements followed in Revit Structure is based on their usage. 

Revit Structure uses five classes of elements:

Host

Host are elements categories that form the basic structure of a building model and include model elements such as structural walls and floors.

Components

Components are the elements that are added to host elements or act as stand-alone elements such as doors, windows, and foundations. Components are used to model building elements that are usually delivered and installed on site, such as doors, windows, furniture, and so on. Components are instances of loadable families and are hosted by other elements, which are instances of system families. For example, a door is hosted by a wall, while a freestanding component such as a desk is hosted by a floor or a level.

Annotations

Annotations are the 2D; view-specific elements that add content to the project documentation such as dimensions, tags, text notes, and so on.

Views

Views represent various orientations of a building such as plans, elevation, sections, 3d views, and so on.

Datum

Datum refers to the reference elements that assist you in creating a building model, which include grids, levels, reference planes, and so on. However they are not visible in all views, if the datum does not intersect a view’s plane (or does not intersect the plane in the correct way). Then it will not be visible in that view.

Image source: http://help.autodesk.com/view/RVT/2014

Source: Autodesk Revit Help, Global etraining

Related post:
Best Practices for Modeling in Revit

Important Notice: End of Sale of New Perpetual Licenses (Autodesk AutoCAD LT Family products)

The changes they’re making 
Autodesk is gradually transitioning new software purchases of our products to subscription options only.
After 31 October 2015, perpetual licenses of the following Autodesk® AutoCAD LT® Family products will no longer be available for sale in selected Asia Pacific countries (Bangladesh, Bhutan, Brunei, Cambodia, China, Hong Kong, India, Indonesia, Korea, Laos, Macau, Malaysia, Maldives, Myanmar, Nepal, Philippines, Singapore, Sri Lanka, Taiwan, Thailand and Vietnam):

• Autodesk AutoCAD LT
• Autodesk AutoCAD LT for Mac®
• Autodesk Inventor LT™
• Autodesk Revit LT™
• Autodesk AutoCAD® Inventor LT™ Suite
• Autodesk Revit LT™ Suite

Customers who purchased perpetual licenses, of Autodesk AutoCAD LT Family products before 31 October 2015, will be able to continue to use that license. Customers who have a perpetual license with Maintenance Subscription (US site) will receive software updates and corresponding benefits for as long as the subscription remains active. New seats of most individual software products, excluding Design and Creation Suites, will generally be available only as pay-as-you-go Desktop Subscription options globally after 31 January 2016.

Desktop Subscription is available as monthly, quarterly, one, two and three-year plans. We will continue to innovate and improve Desktop Subscription products so they more tightly integrate with Autodesk cloud services, and reduce file compatibility issues.

Their commitment to you 

Throughout this period, Autodesk and our partners will work with customers to make this transition from perpetual licenses to Desktop Subscription as smooth as possible, and to deal with exceptional situations accordingly. We will provide as much advance notice as we can so that people can anticipate and plan for these changes. Please refer to the Questions & Answers section below for more detailed information. We will update this site as we progress through the transition. If after reading the details below you still have questions, please visit our Perpetual License Changes Forum (US site) to ask questions or review answers we have given to other visitors.

Why they’re making these changes 

How we design and build the world is changing rapidly, which in turn is changing the tools we use and the ways companies and individuals buy and access software. Our customers have long asked for greater flexibility and more value from their software, and the shift to

Desktop Subscription allows Autodesk to deliver both. With Desktop Subscription you get a simplified product management and deployment experience. Plus, it's easier to introduce new tools and more seats into a project with lower upfront cost and the ability to pay as you go.

We think that the smoothest transition for our customers in selected countries is to take a phased approach as we move to subscription-only software access. This approach is being implemented in Asia Pacific (Bangladesh, Bhutan, Brunei, Cambodia, China, Hong Kong, India, Indonesia, Korea, Laos, Macau, Malaysia, Maldives, Myanmar, Nepal, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, and Vietnam).

Perpetual licenses of Autodesk AutoCAD LT Family products will no longer be available after 31 October 2015. New seats of most individual software products, excluding Design and Creation Suites, will generally be available only as pay-as-you-go Desktop Subscription options globally after 31 January 2016.

To learn more about this policy change, please click here, contact your local Autodesk Authorized Reseller, or contact dts.asean@autodesk.com

Source: autodesk.com