# ISN vs. KEY **URL:** \ **Category:** Forum\ **Tags:** Adabas-Natural, Adabas, Adabas-on-Mainframes, Adabas-Basics-on-Mainframes\ **Created:** [August 4, 2008, 4:32pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78678 "2008-08-04T16:32:33Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![ROHAN\_LOBO](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@ROHAN\_LOBO](https://techcommunity.softwareag.com/u/ROHAN_LOBO)\ **Post date:** [August 4, 2008, 4:32pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78678/1 "2008-08-04T16:32:33Z")
Hi All, I know that ISN is unique.I want to know whether descriptor(key) unigue or is it must be non unigue? If it is a unique, then what is the difference between ISN and KEY? Thanks, Rohan. ---
**Author:** ![Richard\_Bryan](https://avatars.discourse-cdn.com/v4/letter/r/ea666f/32.png) [@Richard\_Bryan](https://techcommunity.softwareag.com/u/Richard_Bryan)\ **Post date:** [October 2, 2008, 12:26am UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78678/2 "2008-10-02T00:26:55Z")
Rohan, ISN is guaranteed to be unique. However, with certain utilities, it can be re-assigned. It is not good to use as a key. Descriptors are built upon data in the file (like customer id number). These descriptors can be defined as unique or not (the default). There is a little overhead with the Unique Option, but it will guarantee that the value is unique within the file. Richard Bryan Database Administrator Austin American-Statesman ADABAS V813 NATURAL V423 PREDICT 452 ---
**Author:** ![system](https://global.discourse-cdn.com/techcommunity/original/3X/c/d/cd19967bb605d28a72d77eb83a1cae22f3df2eb8.svg) [@system](https://techcommunity.softwareag.com/u/system)\ **Post date:** [April 2, 2021, 2:50pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78678/3 "2021-04-02T14:50:42Z")