I know nothing about Informix, I'm new with DB. please give advice.

We are using Ci-sam now, and we need to transfer data in our file to Informix database. This must allow the current application to access to Ci-sam, while some new application will use SQL to access Informix.
I've read about ci-sam blade module, is this the best solution?

Please recommend, thank you.

You hav etwo possibilities. SE (Standard engine) and the C-Isam Datablade. I woul go for the second one, gives you lots more opportunities and features.
SE is a very old C-ISAM file based database server. This is actually an SQL layer on top of C-Isam files. You can access the files with read commands - but there are some locking issues if you want to update from C-isam and from SQL.
The C-Isam datablade has two implementations:

1. Store C-Isam files in the database.
This is actually a unique product. The blade contains C-Isam libraries that you will have to link in your programs. At that time the C-Isam files will access the database in stead of the files. ALl isread calls will be converted to sql calls.
Locking and SQL optimization is done by the database server IDS.

2. Use teh Virtual Table Interface to access the C-Isam files. (not so nice)