What Is Baan 3GL and 4GL?
Also known as: Baan 4GL, Baan 3GL, LN 3GL/4GL
Definition
Baan 3GL and 4GL are the two programming languages of Baan and Infor LN. 4GL is the event-driven script attached to a session and its form fields, while 3GL is the C-like language used for libraries, DAL objects and standalone programs.
Baan 3GL and 4GL Explained
The 4GL language is what makes a session behave. A session script is divided into labelled sections that the runtime calls at defined moments: initialization before the program starts, logic before and after a field is entered or left, handling for each form command the user can invoke, logic around reading and writing the main table, and cleanup at the end. Developers do not write a main loop; they fill in the hooks the framework calls.
The 3GL language is a C-like procedural language used where session context is not appropriate: shared function libraries, data access layer objects that carry business rules for a table, conversion programs, and interface routines. Both languages are compiled into pseudo-code and executed by the bshell, so a 3GL function and a 4GL script section share the same runtime, the same database abstraction and the same embedded SQL-style syntax for selecting and updating rows.
Data access layer objects deserve particular attention because they changed the customization model. When business rules live in a DAL attached to a table rather than in the session script, every path that writes that table - the session, an exchange scheme import, an integration or a custom program - inherits the same validation and defaulting. This is why Baan V and LN moved logic downwards into DALs and why bypassing the DAL during a data load is such a reliable way to create corrupt records.
Development happens against a specific VRC, and code compiled into a derived VRC shadows the standard object beneath it. That is powerful and dangerous in equal measure: it is how a site customizes without touching standard source, and it is also how upgrade projects discover that a standard fix has been silently overridden for years. Modern LN pushes teams towards the extension framework instead, so that standard objects stay untouched and updates apply cleanly.
Why It Matters
- Almost every legacy Baan customization is written in these languages, so migration cost is proportional to how much of it exists.
- Business logic placed in a DAL protects data across every write path, while logic buried in a session script protects only that screen.
- The scarcity of 3GL and 4GL developers is now a staffing risk, not just a rate issue, for organizations on older releases.
- Understanding VRC shadowing explains why standard patches sometimes appear to have no effect on a customized environment.
In Practice
A classic 4GL bug pattern is putting validation only in a field-level hook. It works perfectly for users typing into the screen and fails completely for the same table updated by an exchange scheme, an integration or a batch program. If a rule must always hold, implement it in the DAL for the table, not in the session script.
Frequently Asked Questions
What is the difference between Baan 3GL and 4GL?
4GL is the event-driven scripting language bound to a session and its form: you write logic into predefined sections that the runtime calls at specific moments. 3GL is a C-like procedural language used for shared libraries, data access layer objects and standalone programs where there is no form or session context. Both compile to pseudo-code executed by the same bshell runtime.
Are Baan 4GL skills still relevant for Infor LN?
Yes. Infor LN still runs on the same language and runtime foundation, so a developer who can read and write Baan 4GL and 3GL can work productively in LN. What changes is the tooling and the customization model: development moves into LN Studio, and new work should target the extension framework rather than modifying standard sessions in a derived VRC.
Related Terms
Bshell
The bshell is the Baan and Infor LN virtual machine. It loads compiled pseudo-code for sessions, scripts and reports, executes it, and translates the application's database calls into native SQL through porting set drivers - one bshell process typically serves one user session.
Infor LN Studio
Infor LN Studio is the development environment for Infor LN. It gives developers an Eclipse-based workspace to write and debug 3GL and 4GL code, design sessions, forms and reports, and manage components and VRC software layers against a live LN development environment.
LN Extensions
LN Extensions are Infor LN's supported customization framework: extension scripts and objects attached to standard sessions, tables and business logic through defined extension points, stored outside standard code so vendor upgrades and cloud updates do not overwrite them.
Go Deeper
Baan Modernization ROI Calculator
Build the financial case for leaving legacy Baan: estimate annual savings, payback period, and three-year ROI from a modernization investment.
Baan 4GL Modernization: Strategies for Legacy Code
Baan 4GL modernization strategies: inventory legacy sessions, retire dead code, convert customizations to LN extensions, and de-risk your Baan installed base.
Infor LN Studio Development: Extensions Without Upgrade Pain
Infor LN Studio development guide: 4GL sessions, DALs, LN Extensions, and CDFs - how to customize LN without source modifications that break upgrades.
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Infor LN 4GL Session Script Template
Generate a clean Baan / Infor LN 4GL session script skeleton with declaration, field, choice and table I/O sections.
New to Infor LN and Baan? Start with the Infor LN and Baan guide and toolkit, or plan with Training Path Builder, Upgrade Path Planner, ERP Table and Field Explorer.
Keep exploring
Free tools
- Infor LN 4GL Session Script TemplateGenerate a clean Baan / Infor LN 4GL session script skeleton with declaration, field, choice and table I/O sections.
- Infor LN 4GL Embedded SQL Select GeneratorFill in a table, columns and a where clause and get a Baan / Infor LN embedded SQL select loop with host variables, index ordering and selectempty and selecterror handling.
- Infor LN DAL Script Template GeneratorGenerate a Data Access Layer (DAL) script skeleton for an LN table with object hooks, a field check hook, a mandatory hook and error message handling.
ERP fixes and how-tos
- Infor LN DAL Out of Sync After a Custom Field: Cause and FixInfor LN throws a DAL out of sync error after a custom field is added. Here is why table admin and DAL regeneration must run together, and the fix.
- Infor LN Studio: compile errors when building DAL/4GL codeInfor LN Studio compile errors on DAL and 4GL objects: how to read the build log, common unresolved-reference causes, and when a full rebuild fixes it.
- DB Error 100 in Infor LN and Baan: Record or End of Set Not FoundDB error 100 in Infor LN or Baan means a record or end of set was not found. Learn the causes, how to trace it in the bshell and debugger, and handle it in 3GL.
Guides
- Infor LN BShell Customization GuideMaster Infor LN BShell customization. 4GL programming patterns, session scripting, DLL extensions, and upgrade-safe customization techniques.
- Infor LN BShell Programming: Developer Fundamentals GuideMaster Infor LN BShell scripting with this developer guide covering 4GL syntax, database operations, session hooks, and debugging techniques for BAAN/LN ERP.
- Infor LN Session Programming GuideComplete guide to Infor LN session programming. Session architecture, form design, data handling, and business logic implementation for LN developers.
Integrations
- How to add AI agents to Baan IV and Baan VHow to add AI agents to Baan IV or Baan V: tool layer over read-only database access and AFS, human approval on writes, and an on-prem model. A practical guide.
- How to add an AI chatbot to Baan IV and Baan VAdd an AI chatbot to Baan IV or Baan V: grounded in ERP data and documentation, usable by staff and customers, and able to run fully on-prem with open models.