InterSystems·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Interviewed for a software engineering role at InterSystems and got a fairly deep technical question around XML processing. Not the kind of thing you can wing with surface-level knowledge.

Questions Asked (1)

You have an XML document where some elements contain CDATA sections that are themselves valid XML. Write code to detect these CDATA blocks, strip the wrapper, and inline the inner XML so the whole thing parses as one unified tree. Also explain why standard parsers choke on the original input, what edge cases you need to handle, and how you'd test it.

System DesignTechnical Trade-offsAPI & Integrations

Author's notes

This one took me a second to even parse the premise.

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AI HintsAI Generated

Suggested Approach

Start by explaining why standard parsers treat CDATA as opaque text, then outline a two-pass approach: first parse the outer XML to locate CDATA sections, then parse the inner content as XML and replace the CDATA node with the parsed fragment. Finally, discuss edge cases like nested CDATA, malformed inner XML, and namespace conflicts, and describe a test suite covering these scenarios.

Pro tip: Mention that you'd use a streaming parser (e.g., SAX) for large documents to avoid loading everything into memory, and that you'd preserve the original CDATA boundaries for round-tripping if needed.

1. Explain parser behavior

Describe how standard XML parsers treat CDATA as character data, not markup, so they don't parse the inner XML, leading to a tree where the CDATA content is a text node. This causes the unified tree to be incorrect.

2. Detection and extraction

Use a DOM or SAX parser to find CDATA sections. For each, extract the text content and attempt to parse it as a standalone XML fragment, handling any parsing errors.

3. Replacement and inlining

Replace the CDATA node with the parsed fragment's nodes, ensuring proper merging of namespaces and attributes. If using DOM, import nodes into the main document.

4. Edge cases

Handle nested CDATA (CDATA within CDATA), malformed inner XML, multiple CDATA sections, namespace prefix conflicts, and encoding issues. Decide whether to fail, skip, or attempt repair.

5. Testing strategy

Write unit tests with various inputs: valid inner XML, invalid inner XML, nested CDATA, large documents, and namespace collisions. Verify the output parses as a single tree and matches expected structure.

Key Points to Mention

CDATA sections are treated as raw text by XML parsers, so inner XML is not parsed.
Two-pass parsing: outer parse to find CDATA, inner parse to convert to nodes.
Namespace handling: inner XML may use prefixes not declared in outer document, requiring namespace resolution.
Edge cases: nested CDATA, malformed inner XML, multiple CDATA blocks, and large documents.
Testing: unit tests for valid/invalid inner XML, round-trip validation, and performance tests.
Trade-offs: DOM vs SAX for memory vs simplicity; error handling strategies (fail fast vs best-effort).

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.