How do you extract data from legacy systems that lack APIs?

Extracting data from legacy systems without APIs typically involves direct database access, file parsing, or UI automation. The first step is identifying where the data resides—whether in relational databases, flat files, or proprietary storage formats. For database-driven systems, tools like ODBC/JDBC connectors can enable direct SQL queries if credentials and permissions are available. For example, connecting to an old Oracle database using Python’s cx_Oracle library allows developers to run SELECT statements and export results to CSV or JSON. If the database schema is undocumented, reverse-engineering table relationships through trial and error or using database introspection tools becomes necessary.

When direct database access isn’t feasible, file-based extraction is a common fallback. Many legacy systems export reports or data dumps in fixed-width, CSV, or even proprietary binary formats. Developers can write scripts to parse these files using languages like Python or Perl. For instance, a COBOL system might generate nightly transaction logs in a fixed-width format, which a Python script using the struct module could decode. Log files or print spooler outputs (e.g., PRN files) are also viable sources, though parsing them may require regex patterns to isolate relevant data. In cases where files are encrypted or use outdated encodings (e.g., EBCDIC), additional conversion steps are needed.

For systems where data is only accessible through the user interface, screen scraping or terminal emulation becomes necessary. Tools like Selenium or AutoIt can automate navigation through green-screen interfaces (common in mainframes) and extract text from specific screen coordinates. For example, a legacy inventory system might require simulating keystrokes to navigate menus and scrape tabular data using AutoHotkey. Alternatively, terminal emulators like TN3270 for IBM mainframes can capture screen output and parse it programmatically. This approach is fragile, as UI changes can break scripts, but it’s often the only option for closed systems. In all cases, data validation and error handling are critical to ensure accuracy, especially when dealing with inconsistent legacy data formats.