Migration planning with graphs

System and data migration is a critical part of many long-lived software systems.

At first, migration may look simple. We move data from the old system, convert it, and load it into the new system. In reality, it is rarely that easy.

A migration project often reveals problems that have been hidden for years. The data may not match the current specifications. The source code may have changed, while the documentation was not updated. Data patches may have been applied incorrectly. Character encoding issues may appear only when real production data is moved. The final cutover timing can also become a major risk.

I have been involved in many migration projects. In my experience, migration almost never works perfectly on the first attempt.

This does not mean migration is impossible. It means migration needs careful checking before, during, and after the move.

One important step is to examine the data carefully. Another is to check whether the relationships in the existing database are still correct. In relational databases, foreign keys may not describe all real business rules. Some relationships may exist only in application logic. Some records may look fine by themselves, but become inconsistent when connected to other records.

This is where graph technology can help.

By modeling tables, records, dependencies, references, and validation rules as a graph, we can see the structure of the data more clearly. Problems that are difficult to find in separate tables can become easier to understand as relationships.

For example, graph-based validation can help find:

• child records without a valid parent record
• records that refer to old or invalid codes
• incorrect relationships created by data patches
• dependencies that affect the migration order
• data that needs special handling during cutover
• character encoding problems that appear in specific data paths

The purpose is not simply to store migration data in a graph database. The purpose is to use graph modeling as a practical validation and investigation tool.

In migration planning, many important questions are about relationships.

• What depends on this data?
• Which records must be migrated together?
• What will break if this mapping is wrong?
• Which inconsistencies are isolated?
• Which inconsistencies affect other parts of the system?
• What should be checked before the final cutover?

Graphs are well suited for these questions.

A graph-based validation model can also help communication. Engineers, domain experts, and project stakeholders can discuss migration risks using the same structure. It can become a practical checklist for data cleansing, migration order, test cases, and post-migration verification.

Migration is not only a data transfer problem. It is also a knowledge problem.

An old system contains many implicit rules, exceptions, patches, and historical decisions. A successful migration needs to make those relationships visible enough to check, discuss, and improve.

Graph technology can support that process.

日本語補足：

システム移行・データ移行は、単にデータをコピーする作業ではありません。データ不整合、仕様書と実装のずれ、データパッチ、文字コード、移行順序、切替タイミングなど、多くの問題が関係します。

これらの関係性をグラフとして整理することで、親レコードが存在しない子レコード、誤った参照、移行順序の依存関係、検証すべきデータのつながりを見つけやすくなります。

Migration is not just ETL. It is validation, modeling, and risk reduction.