First of all, be very careful when updating schema as this could potentially wipe out existing content.
These are relatively safe:
- add a new field
- update description on exsiting field
- change display type between radio, drop-down, or text select (might want to test this first)
- add additional options (or add keywords to a category used by a text field)
- change xml name of a field or root
- change a schema namespace
- changing mandatory options (semi-dangerous, this may cause validation issues as well as confuse editors)
- change options (old existing selections will not change, except for keywords, at least with Tridion 2011)
None. No effect on content... yet!
The catch is that the component will validate against the current schema when they are next individually opened and saved. This has some possibly unexpected consequences on your content.
- Changes from templates, component presentations, and pages won't show until components are updated (open, possibly make a small change like adding a space to the title, and saving again)
- Content looks okay on the websites, but users complain about new or updated components losing fields, having to enter new mandatory fields, etc
- Content fields "disappear" upon open (when one of the "dangerous" updates was done)
A change to a keyword or selection option does not change preselected items in existing components, which are stored as text in the XML-based component data.(not true last I checked with Tridion 2011)
Keep an eye out, especially if a template or component issue only affects some but not all content. This could be a sign that only newer and modified components have the issue, which is a hint that there may have been a schema change.If you happen to make an accidental change, consider reaching out to technical support or your implementation team right away. If you haven't updated the existing content, there might be hope by undoing the change and/or using content porter to preserve the existing (old) components. Since content porter validates against schema, this one might be tricky.
Have fun, but be careful when updating your schema!