What are some of the benefits and drawbacks of changing cataloging rules from AACR2 to RDA? Additionally, how is this going to affect the millions of MARC records currently in AACR2 rules? When is the change expected to roll out to all libraries?
Starting from the end, because it's easier:
When is the change expected to roll out to all libraries? Magic 8-Ball says CANNOT PREDICT NOW. In addition to the AACR2 to RDA transition, there's a MARC to linked-data/relational-database (depends on whom you ask) transition underway. Leaving aside that neither transition's goal state is fully-mapped yet, when the transitions hit a library near you depends heavily on ILS vendors, who just now are giving the whole thing a complete miss.
How is this going to affect the millions of MARC records currently in AACR2 rules? Magic 8-Ball says REPLY HAZY, TRY AGAIN. The current claim as I understand it is that RDA records and AACR2 records can more-or-less happily coexist in the same catalog. Whether that continues to be the party line given the MARC-to-whatever transition is under debate (the BIBFRAME list is the place to be; see also Karen Coyle's blog).
What are some of the benefits and drawbacks of changing cataloging rules from AACR2 to RDA?
Like Dorothea, I'm going to work backwards through your questions.
When is the change expected to roll out to all libraries? Which part of the change? The change from AACR2 to RDA? Well, there's several answers to this.
The change in the National Authority File will be March 31, 2013. There will be some headings in the NAF that are still AACR2 and will need manual clean up, but the vast majority of headings will be "RDA compliant" and will require no maintenance. All new authority headings added to the NAF from April 1, 2013 on MUST be RDA headings.
The Library of Congress is going one step further, and switching ALL cataloging to RDA on the same timeline. They are currently in process of training all their catalogers so they will be ready for the March 2013 deadline. The training materials are available for free here: http://www.loc.gov/catworkshop/RDA%20training%20materials/index.html Information on LC's RDA plans is here: http://www.loc.gov/aba/rda/
When asked at ALA, most libraries intend on making the change from AACR2 to RDA cataloging in the same time frame, as in the first quarter (or half) of 2013.
Information from the PCC (Program for Cooperative Cataloging, aka BIBCO/CONSER/NACO/SACO) on implementation can be found on the PCC website: http://www.loc.gov/aba/pcc/rda/RDA%20Implementation.html There is no "hard and fast" deadline for the switch. It's anticipated that once libraries start switching (and several libraries that participated in the test have continued to catalog in RDA so it's already started) it will have a snowball effect and more and more libraries will switch to RDA.
How is this going to affect the millions of MARC records currently in AACR2 rules? Short answer: it's NOT. RDA was written so that AACR2 records will NOT have to be re-cataloged. AACR2 and RDA are perfectly capable of playing nice with each other and living side by side.
That said, there are task groups working on the idea of "hybrid" AACR2/RDA records to fully utilize the benefits of RDA. The goal is to enhance the AACR2 records, without affecting their bibliographic integrity.
What are some of the benefits and drawbacks of changing cataloging rules from AACR2 to RDA? Things like relationships in RDA are where the "real" benefits live. It's a step towards linked data. One of the biggest differences is just the way you think about a resource when you describe it. But we are currently prevented from fully utilizing RDA by the limits of MARC. I second Dorothea's recommendations to read/listen to Karen Coyle and others on this topic.
The change from MARC to whatever comes next (the Bibliographic Framework initiative http://www.loc.gov/marc/transition/ ) will have a whole different impact and hopefully we'll be able to fully utilize the benefits of RDA.