# ISN vs. KEY

**URL:** <https://techcommunity.softwareag.com/t/isn-vs-key/78674>\
**Category:** Forum\
**Tags:** Adabas-Natural, Adabas, Adabas-on-Mainframes, Adabas-Basics-on-Mainframes\
**Created:** [August 4, 2008, 4:31pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78674 "2008-08-04T16:31:28Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**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, 4:31pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78674/1 "2008-08-04T16:31:28Z")

</div>

I believe there is some technical problem, so the same post that i posted is appearing 3 times. sorry for the inconvnience…

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.

---

<div class="post-metadata">

**Author:** ![Curtis\_Pew](https://avatars.discourse-cdn.com/v4/letter/c/5f9b8f/32.png) [@Curtis\_Pew](https://techcommunity.softwareag.com/u/Curtis_Pew)\
**Post date:** [August 4, 2008, 6:12pm UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78674/2 "2008-08-04T18:12:28Z")

</div>

When you define a descriptor you may specify that it be unique. If you don

---

<div class="post-metadata">

**Author:** ![Douglas\_Kelly](https://sea1.discourse-cdn.com/techcommunity/user_avatar/techcommunity.softwareag.com/douglas_kelly/32/102_2.png) [@Douglas\_Kelly](https://techcommunity.softwareag.com/u/Douglas_Kelly)\
**Post date:** [August 5, 2008, 2:54am UTC](https://techcommunity.softwareag.com/t/isn-vs-key/78674/3 "2008-08-05T02:54:23Z")

</div>

It is your choice to define a descriptor or superdescriptor as unique. You can have more than one unique descriptor on a file (I don’t recommend it, but it is “legal” for Adabas). It is also legal (again I don’t recommend it) to allow null values for a unique descriptor. An ISN will always exist whether or not you use it directly and only one per record.

A unique descriptor can be alphanumeric, numeric or any valid Adabas format. An ISN is always an internal number assigned by Adabas. You can update the values, including unique descriptors, of a record, but you can’t update the ISN (of course, you can delete it and add it again).

So, yes, there is some overlap between the ISN and a unique descriptor, but one (ISN) is a system-managed value and the other is application managed. Either can uniquely identify a given record.

---

<div class="post-metadata">

**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/78674/4 "2021-04-02T14:50:42Z")

</div>