how to define a writeable Global variable in transaction？

hi all,

  Now i have a case as that when i get data from a source ,such as PCo/Oracle ，

  i just want it is kept  and i could get it regular intervals when i execute this transaction or another one.

  As the data also should be writeable , so i could not use Global variate.

  is there any solution ？

  and what's the life cycle of transaction, is it died automatic after execute?

  Thank you in advance!