Siemens Digital Industries Software · Software Engineer
Updated · 2026-09-24

Siemens Digital Industries Software Software Engineer
Interview Guide

THE 60-SECOND BRIEF

As a Software Engineer at Siemens Digital Industries Software, you are responsible for constructing the foundational technology that powers the world’s leading industrial enterprise solutions. Siemens software enables manufacturers, aerospace leaders, automotive pioneers, and semiconductor designers to create digital twins, simulate complex physical phenomena, and automate advanced production environments. Whether you are building high-performance geometry kernels for CAD software, developing physical simulation engines in Simcenter 3D, or engineering electronic design automation (EDA) tools, your code will directly drive global industrial innovation.

For a design discussion, a catalogue of architectures is worth less than the ability to turn a vague requirement into a data model and an API contract. A box diagram with no schema under it collapses at the first follow-up question.

Siemens Digital Industries Software candidates report 4 rounds · ≈ 3-5 weeks. The stages below are what candidates describe, not a published process.

Bound blast radius with per-tenant concurrency limitsMake every write idempotent under client retriesBuild at-least-once pipelines with explicit deduplication horizons

37 min read

Browse Software Engineer questions

See the practice prompts

1Candidate experiences ↗Read their reports
15Practice promptsAcross five skill areas
3With worked solutionsIncluded in the practice prompts

As a Software Engineer at Siemens Digital Industries Software, you are responsible for constructing the foundational technology that powers the world’s leading industrial enterprise solutions. Siemens software enables manufacturers, aerospace leaders, automotive pioneers, and semiconductor designers to create digital twins, simulate complex physical phenomena, and automate advanced production environments. Whether you are building high-performance geometry kernels for CAD software, developing physical simulation engines in Simcenter 3D, or engineering electronic design automation (EDA) tools, your code will directly drive global industrial innovation.

The impact of this role extends across millions of engineers and thousands of enterprise organizations worldwide. You will solve non-trivial software engineering challenges involving massive data sets, intense computational constraints, high-throughput memory management, and cloud-native microservices architectures. Unlike web application development in standard SaaS businesses, software engineering at frequently sits at the intersection of deep computer science fundamentals, mathematical optimization, and domain-specific engineering logic like computational fluid dynamics, mechatronics, and acoustics.

This environment requires high precision, analytical rigor, and a deep appreciation for low-level software fundamentals. Expect to work in multidisciplinary teams alongside domain experts, build resilient codebases meant to scale over decades, and solve deep technical problems. The company values engineers who are curious, methodical, and capable of translating complex physical or structural rules into performant, clean software architecture.

01

Resume Screening

reported

Before anything technical happens, someone has to decide which rung of the ladder your loop is calibrated to, and that decision sets the bar for every round after it. It comes from how you describe scope, not from your title, because titles do not convert cleanly between companies. The weak version of the answer is team size and years. The strong version names the largest change you shipped where nobody reviewed the design, what would have broken if you had been wrong, and what you were paged for. Get the level said out loud on this call, because the range and the loop both follow from it.

What to demonstrate

  • Whether the scope in your own account maps onto a level the team actually has an opening at, so a mismatch ends the process cheaply rather than after four interviewers have spent a day
  • Whether your title needs re-mapping: the same word describes very different amounts of independent decision-making at a twenty-person company and a ten-thousand-person one
  • Whether your compensation expectation can be filled at that level in the structure the role pays in, which is why the number gets asked for before any engineer is scheduled

How to prepare

  • Write down two changes from the last two years: the largest one you designed with nobody reviewing the design, and the largest one where someone more senior did. Lead with the first when scope comes up, and be ready to say which parts of the second were yours
  • Ask which level the loop is calibrated to and what changes at the level above it, then plan your weeks from that answer rather than from the posting
  • Settle a total-compensation range beforehand with the split named, base against bonus against equity and its vesting period, so a question about numbers gets a number instead of the word market
PracHub interview research ↗
02

Technical Assessments

reported

What this round decides is narrow: whether you can produce code that runs and is correct on inputs nobody showed you. An elegant solution that does not compile scores below a plain one that does, so write a correct brute force first, say out loud that you know its cost, and improve it with the working version still on screen. What separates strong answers is who finds the broken case. Trace your own code against an empty input, a single element, and duplicate keys before you say you are finished, because being told is far more expensive than noticing.

What to demonstrate

  • Whether degenerate inputs get checked without being asked for: an empty collection, one element, every element equal, and the extreme value the input type allows
  • Whether the complexity you state matches the code you actually wrote, including a sort or a copy sitting inside a loop
  • Whether the finished answer is verified against the worked examples before you call it done, rather than assumed correct because the code reads correctly

How to prepare

  • Take five problems you have already solved and, without running anything, write down what each returns for empty input, a single element, and all-duplicates. Then run them and count how many you predicted wrong.
  • Drill the brute force as its own skill: on ten problems, write only the obviously-correct slow version and time how long it takes to get it passing. If that is more than a few minutes, that is what to practise, not the optimal version.
  • Add a fixed last step before you submit anything, reading only the loop bounds and the initial value of each accumulator, which is where most off-by-one errors live
PracHub interview research ↗
03

Behavioral Interviews

reported

What you say here is written down by each interviewer and compared afterwards, so the unit of evaluation is a claim someone else could check, not a well-told narrative. Two things make a story checkable: detail only a participant would hold, and a clean line around which part was yours. Vague ownership is the usual failure and it is usually accidental, because engineers say we about the team's work and we about their own, so the thing they personally built disappears into the plural. Name the part you wrote, and name who did the rest.

What to demonstrate

  • Whether your details are ones a participant would hold and an observer would not: the constraint that ruled out the obvious approach, the first attempt that failed, the person who objected and on what grounds
  • Whether ownership survives a direct question, since a follow-up to we decided is routinely who decided, and an answer that stays plural at that point is read as the work belonging to someone else
  • Whether the numbers you quote are ones you would say identically to a former colleague with the dashboard open

How to prepare

  • Go through each story replacing every we with either I or a named role (the on-call engineer, the reviewer, the other team) and check the story still holds together. Wherever it stops making sense you have found a part you cannot actually speak to
  • Open the artefacts for two of your stories, the pull request, the design doc, the incident notes, and read them for dates and figures you have been rounding in the retelling. Correct your version to match
  • For each story write the single sentence you would least want repeated to a former teammate, then either make it accurate or take it out
PracHub interview research ↗
04

Presentations

reported

You cannot drill a format you do not know, so put the preparation into material that travels. Three pieces of your own work, each rehearsed until you can take a follow-up you did not anticipate, will carry a conversation or a code walkthrough equally well. Specificity is what separates that from filler. A number needs its definition before it means anything: a p99 is over some window and measured at some hop, and a server-side figure excludes the queueing and network time a client would see. The number you cannot qualify is the one to leave out.

What to demonstrate

  • Whether your examples carry detail only someone who did the work would hold, such as what the binding constraint actually was, which alternative you rejected and why it was worse, and what you measured on each side of the change
  • Whether a number survives one follow-up, meaning you can say what it was measured over and whether it moved because of your change or merely alongside it
  • Whether a failure is described with the specific change that followed it, rather than a lesson stated in general terms
  • Whether your part in a team effort is stated accurately, including what other people did

How to prepare

  • Write a page on each of three projects covering the constraint, the option you rejected, the measurement before and after, and what went wrong. Cut any line you cannot take a follow-up on, since you are writing the parts you will be pressed on rather than a summary.
  • Recover the real figures while you still have access: request volume, data size, latency with its percentile and window, team size, timeline. Note where each came from, whether a dashboard, a design document or memory, and mark the estimates so you can say which they are out loud.
  • Take your weakest project story to someone who works in a different area and have them ask why four times in succession. The point where you run out of answer is the part to go and re-read before the round.
PracHub interview research ↗

1 candidate reports. Individual accounts describe a particular role and hiring cycle.

Software Engineer

Siemens Digital Industries Software Software Engineer Interview Experience: C++ and teamwork discussion

Technical ScreenOutcome: offer

After the recruiter call, I had a smooth, organized interview that stayed professional throughout. I started by introducing my background, the projects I had worked on, and the technical experience I could bring to the role. The questions then moved into programming basics, especially C++ fundamentals and object-oriented concepts. They also wanted to hear how I approach problem-solving and teamwo…

Read full experience

PracHub editorial advice for the preparation topics above.

01

Checking a quota with a select and then writing

Under read-committed isolation, two concurrent transactions both observe a count below the limit and both insert, so the limit is exceeded by exactly the concurrency. Repeatable read does not rescue it either: it provides a stable snapshot, and this is write skew, which snapshot isolation permits by design. The options are serialisable isolation, which detects the conflict and aborts one transaction with a serialisation failure and therefore obliges the caller to retry; a single statement with the predicate inside the write; or a constraint that makes the surplus insert fail outright. The reason this pattern survives review is that it is correct in every test that runs one request at a time.

02

Paginating a growing table with limit and offset

Two unrelated defects share the idiom. Correctness: rows inserted or deleted between page requests shift the window, so a consumer walking an export skips rows and sees others twice, which for a customer-facing sync is silent data loss rather than an error anyone notices. Cost: the database still produces and discards the skipped rows, so page N costs time proportional to N times the page size and a deep page on a large table degrades from milliseconds to seconds. Keyset pagination over a stable, unique, indexed ordering -- where (created_at, id) < ($1, $2) order by created_at desc, id desc limit $3 -- is constant-cost per page and immune to shifting, on the precondition that the cursor columns never change value for a row, which disqualifies updated_at as a cursor.

03

A cache with no invalidation story

Say how an entry goes stale, how long you can serve it stale, and what happens when many requests miss the same key at the same instant. One popular key expiring under load sends every concurrent request to the origin together; single-flight coalescing, jittered expiry, or serving stale while revalidating are the standard answers.

04

Listing technologies instead of trade-offs

Name the property the design needs first, such as ordered range scans, multi-entity transactions, cheap appends, or a predictable p99, then pick something that provides it and say what it gives up in exchange. Almost any component is defensible once you state the requirement it satisfies and the one it sacrifices.

Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.

12 technical prompts3 include a worked solution

Explain your approach to solving binary tree traversals and dynamic pr…

medium
data structures and algorithms

Explain your approach to solving binary tree traversals and dynamic programming problems under strict memory limits.

Approach
  1. Choose the data structure from the access pattern, not from familiarity.
  2. Restate the input: its shape, its size, and what is guaranteed about it.
  3. State the target complexity and say which constraint rules the naive version out.
Follow-up
  • What is the worst case, and how likely is it on real data?
  • How does this change if the input no longer fits in memory?

Debug a given C or Python code snippet live, identifying memory leaks,…

medium
data structures and algorithms

Debug a given C or Python code snippet live, identifying memory leaks, index-out-of-bounds errors, or concurrency race conditions.

Approach
  1. State the target complexity and say which constraint rules the naive version out.
  2. Choose the data structure from the access pattern, not from familiarity.
  3. Restate the input: its shape, its size, and what is guaranteed about it.
Follow-up
  • How does this change if the input no longer fits in memory?
  • Which test case would catch an off-by-one here?

Solve a classic searching problem on a custom collection, evaluating t…

medium
data structures and algorithms

Solve a classic searching problem on a custom collection, evaluating time complexity using Big-O notation.

Approach
  1. State the target complexity and say which constraint rules the naive version out.
  2. Choose the data structure from the access pattern, not from familiarity.
  3. Walk one small example through your approach before writing the whole thing.
Follow-up
  • Which test case would catch an off-by-one here?
  • What is the worst case, and how likely is it on real data?

Parse and verify a timestamped multi-signature webhook header

easyWorked solution
parsinghmacconstant-time-comparereplay-protection

An inbound webhook carries a signature header of at most 1 KiB shaped t=<unix seconds>,v1=<64 hex chars>, with up to five v1 values during secret rotation and possibly unknown scheme keys. You hold the raw request body bytes and the currently active signing secrets. Write the parser and the verifier: accept when any active secret reproduces a signature and the timestamp is within a five-minute tolerance in either direction, reject otherwise. Single left-to-right pass over the header, no regular expression. State what is inside the MAC and why.

Approach
  1. Parse in one scan: split on ,, then on the first = only, since a value may itself contain = under a future scheme. Accept t exactly once and treat a second t as a reject rather than last-wins. Push every v1 onto a short list and ignore any other key, so a v2 can be introduced later without breaking this verifier.
  2. Say what is signed: HMAC-SHA256 over the exact byte string <t>.<raw body bytes>, yielding 32 bytes or 64 hex characters. The timestamp sits inside the MAC because otherwise an attacker replays yesterday's body with its still-valid signature and only has to edit the header timestamp.
  3. Hash the bytes as received. Verifying against a re-serialised JSON body is the usual defect: key order, whitespace and number formatting all change the bytes while the parsed objects compare equal, so signatures fail for honest senders and the popular 'fix' is to stop checking.
  4. Compare in constant time over fixed-length digests. Decode the hex to 32 bytes, accumulate acc |= a[i] ^ b[i] across the whole length, and test acc == 0 at the end. Evaluate every candidate without an early exit; at five candidates that is five HMACs over the body, linear in body size and negligible beside the network.
  5. Apply the tolerance as a two-sided bound, rejecting when |now - t| > 300 seconds. A sender whose clock runs ahead of yours is an ordinary case, and an unbounded future timestamp is a free replay window.
  6. Complexity: O(L) over the header producing k candidates, plus k HMACs at O(|body|) each. Space is O(k) beyond the body itself. Do the cheap rejections, including the tolerance check, before any cryptography runs.
Worked solution 15 min
  1. Write the grammar on one line before coding: header := field (',' field)*, field := key '=' value, split on the first = only.
  2. Implement the parser to return {t: int, v1: [hex, ...]}, rejecting a missing t, a duplicate t, any v1 that is not 64 hex characters, and a header over 1 KiB, all before any cryptography runs.
  3. Implement the verifier: for each active secret compute HMAC-SHA256(secret, f'{t}.'.encode() + raw_body), compare it in constant time against each parsed v1, and OR the results with no early exit.
  4. Test with a valid signature; the same body with t moved 400 seconds into the past; the same body with t 400 seconds into the future; a header carrying an unknown v2= alongside a valid v1; and a body re-serialised with different JSON key order.
EXPECTED RESULTThe valid case accepts. Both out-of-tolerance cases reject, including the future one. The unknown `v2` field is ignored and the `v1` still verifies. The re-serialised body fails, which is correct and is exactly why the raw bytes must be retained.
Follow-up
  • The body is 40 MB. What changes about where you verify, and what can you do before the whole body has arrived?
  • A customer reports that signatures fail for exactly the requests whose body contains a non-ASCII character. What is your first hypothesis?
  • How do you rotate the signing secret with no failed deliveries, and how long do both secrets stay live?

Four days sample coding, design, fundamentals and the practical rounds at deliberately shallow depth, which is enough to surface the topics you did not know were in scope. That map, rather than a guess made on day one, decides where the last three days go.

Small steps. Visible outcomes.0 / 7 completed
ONE WEEK · YOUR PACE

Prepare, practise & reflect

One practical outcome each day. Spend longer where you need it.

0 / 7 done
01Coding, one pass at shallow depth
  • Solve one problem from each of six families, an array with two pointers, hash counting, binary search, a tree traversal, a graph traversal and one dynamic program, under a hard twenty-minute cap with no extensions, marking each finished, late, or stalled.
  • For every stall, write the exact move you could not make rather than the subject, so the note reads could not turn the recurrence into a loop rather than bad at dynamic programming.
  • Fix nothing today. The value of the pass is the unfixed record.

Deliverable: Six timed attempts marked finished, late or stalled, each stall carrying a named blocking move.

Practice prompt ↗Practice prompt ↗Practice prompt ↗Worked solution ↗
02Design, one pass at shallow depth
  • Spend twenty minutes each on three different shapes, a read-heavy feed, a write-heavy ingest path, and something needing a transaction across two entities, stopping each at requirements, interface and data model.
  • After each, write the first question you could not answer, which is usually a number you could not estimate or a failure mode you had no vocabulary for.
  • Mark which of the three you would be most relieved not to be asked, and treat that as data rather than as a preference.

Deliverable: Three shallow designs, each with the first unanswerable question written at the bottom.

Practice prompt ↗Practice prompt ↗
03Fundamentals and the practical rounds
  • Answer eight short questions in writing at four minutes each, covering the material that fills the gaps between the big rounds: what happens between a URL and a rendered page, what an index costs on write, when a process is preferable to a thread, and what conditions a deadlock requires.
  • Do one thirty-minute practical task of the kind a take-home compresses: read an unfamiliar two-hundred-line file and write what it does, what you would change, and the one thing you remain unsure of.
  • Score every answer fluent, correct but slow, or absent, and keep the absent ones visible.

Deliverable: Eight scored short answers and one written reading of unfamiliar code.

Practice prompt ↗Practice prompt ↗
04The rounds that are about you, and the map
  • Deliver three behavioural answers aloud against a timer, a conflict, a failure you owned, and a decision made without enough information, marking any that ran past three minutes or contained no number.
  • Assemble the map: every marked item from days one to three on a single page, sorted by how likely it is to appear in your loop rather than by how uncomfortable it felt.
  • Choose exactly two areas for the remaining three days and write down what you are deliberately abandoning.

Deliverable: A one-page scored map of the whole surface area with two areas chosen and the rest explicitly abandoned.

Practice prompt ↗Practice prompt ↗Worked solution ↗
05First chosen area, to the depth you skipped
  • Work the higher-ranked area in four focused blocks, choosing items one level above where you stalled rather than repeating what already works.
  • After each block write the rule you extracted in one sentence with its precondition attached, since a rule carrying no precondition is exactly what fails under a variation.
  • Re-attempt the day-one or day-two item that exposed this area and compare against the original timing.

Deliverable: Four worked blocks, a timed re-attempt against the original, and three one-sentence rules with preconditions.

Practice prompt ↗Practice prompt ↗
06Second chosen area, where the gap is coverage rather than speed
  • Treat the second area differently from the first. Day five drilled something you could already half-do; this one is usually a topic you had simply never met, so build one worked reference example end to end and keep it, rather than attempting six problems badly.
  • Write down the vocabulary you were missing on day two or three, five terms at most, each with the one sentence that makes it usable in an answer rather than the textbook definition.
  • Redo the shallow attempt that exposed this area and note whether you now fail later in the problem, because moving the failure point is the realistic gain from a single day and is worth more than a score that did not change.

Deliverable: One worked reference example for the newly covered area, a five-term vocabulary list, and a note on where the failure point moved.

Practice prompt ↗Practice prompt ↗
07Reassemble the loop
  • Sit two rounds back to back with no gap, ordering them so the area you chose second comes last, because the map was built from rested, isolated attempts and the loop will reach your weaker area when you are already spent.
  • Write where the second round suffered from the first, which is normally the point at which structure collapses into narration.
  • Reduce the week to one page holding only the rules you can state without reading them.

Deliverable: Mock notes on cross-round carryover plus a one-page card of rules you can recite from memory.

Practice prompt ↗Practice prompt ↗Worked solution ↗

Expand any day for tasks and deliverables. Your progress is saved on this device.

For anything that touched live traffic, be ready to say how you would have undone it: a flag, a staged rollout, dual writes with the old path still authoritative. Once the old column is dropped or the source rows are overwritten there is no reverse, so name what you kept a copy of and for how long.

Tell me about a time you made a significant mistake while writing or d…

medium
behavioural and engineering judgement

Tell me about a time you made a significant mistake while writing or deploying software, and explain how you resolved it and prevented recurrence.

Approach
  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Close with what you would do differently, concretely.
Follow-up
  • How did you know your change caused the improvement?
  • What would you do differently if you ran that again?

How do you prioritize conflicting technical debt, bug fixes, and featu…

medium
behavioural and engineering judgement

How do you prioritize conflicting technical debt, bug fixes, and feature work in an agile development sprint?

Approach
  1. State the situation in two sentences and spend the rest on the reasoning.
  2. Name the disagreement and how you resolved it with evidence.
  3. Give the blast radius: what could have broken, and what you measured.
Follow-up
  • What did you decide not to do, and why?
  • What would you do differently if you ran that again?

Ship metered billing with a named deduplication horizon

medium
technical debtdeduplicationdeadline pressuredetectors

Metered billing must be on in three weeks. usage_event is partitioned daily, so its unique index must include the partition key and deduplicates only within a day: a producer retry that crosses midnight, or a replay run a week later, gets through. A cross-partition dedup store is two weeks you do not have. Describe shipping with debt you named in advance: what you shipped, what you wrote down, the detector you added, the trigger and date for paying it off, and what you would have refused to ship under the same pressure.

Approach
  1. Show you can separate the two kinds of debt, because that distinction is what the question actually probes. Debt that costs engineering time later is shippable on a deadline. Debt that silently corrupts a number a customer gets charged for is not shippable unless the corruption is detectable, and detectability is the whole negotiation.
  2. Make the exposure narrow and measured rather than gestural. The hole is duplicates whose occurrences straddle a UTC day boundary, plus any replay older than partition retention. Measure it before arguing about it: how often an idempotency_key recurs at all, and the distribution of the gap between first and last occurrence. If the ninety-ninth percentile of that gap is four minutes, the residual risk is a small band around midnight and you can say so numerically.
  3. Add the detector before the feature, not after. A nightly job counting keys that appear in more than one partition is one grouped scan over recent partitions, and it converts a silent overcount into a page. State what it costs to run and what it fires on.
  4. Buy the cheap half of the real fix immediately: extend partition retention so the dedup horizon exceeds the producer's maximum retry window plus the longest replay you intend to support. That reframes retention as a correctness parameter rather than a storage cost, which is the sentence you need on record before someone optimises the bill.
  5. Make repayment mechanical instead of aspirational: a dated entry with a named owner, plus a threshold that pulls the date forward — first detector hit above N events, or first customer dispute. Debt with a trigger gets paid; debt with only a date does not.
  6. Answer the second half honestly by naming what you would refuse under identical pressure: the sealing path, because a sealed row is frozen and a wrong number there stops being a bug and becomes an adjustment line, a dispute and an audit question.
Follow-up
  • The detector fires on forty duplicate events for one tenant, and two of their invoices have already sealed. What happens next?
  • Whom did you tell that the billing numbers had a known hole, and in what words?
  • Finance asks you to cut storage by shortening partition retention. What do you say, and to whom?
  • 01

    Tell me about a time you made a significant mistake while writing or deploying software, and explain how you resolved it and prevented recurrence.

  • 02

    How do you prioritize conflicting technical debt, bug fixes, and feature work in an agile development sprint?

  • 03

    Metered billing must be on in three weeks. usage_event is partitioned daily, so its unique index must include the partition key and deduplicates only within a day: a producer retry that crosses midnight, or a replay run a week later, gets through. A cross-partition dedup store is two weeks you do not have. Describe shipping with debt you named in advance: what you shipped, what you wrote down, the detector you added, the trigger and date for paying it off, and what you would have refused to ship under the same pressure.

PracHub interview preparation framework ↗
Is this an official Siemens Digital Industries Software interview guide?

No. It is PracHub's own research and practice material for the Software Engineer role at Siemens Digital Industries Software. Rounds and questions reflect what candidates have reported, not a process Siemens Digital Industries Software has published, and they change over time. Confirm the current format and scope with your recruiter.

PracHub interview research ↗
How technical are the interviews at Siemens Digital Industries Software compared to typical tech companies?

The technical rigor focuses heavily on practical computer science fundamentals, low-level language mechanics, and object-oriented principles rather than purely tricky algorithmic puzzles. You are more likely to be asked about dynamic memory, C++ virtual functions, or design patterns than niche LeetCode Hard tricks, though solid algorithmic proficiency is still tested.

PracHub interview research ↗
Do I need prior background in mechanical engineering, CAD, or physics simulation to qualify?

No, a formal degree or background in physics or mechanical engineering is generally not required unless specified for specialized research roles. Siemens values solid software engineering, mathematical logic, and analytical capabilities; team members will guide you on domain-specific concepts as you onboard.

PracHub interview research ↗
How long does the Siemens interview process take from start to finish?

The hiring process generally takes between two and five weeks, depending on the department, team availability, and geographic region. Some specialized teams move quickly over one to two weeks, while enterprise software pipelines with panel evaluations can stretch slightly longer.

PracHub interview research ↗
What programming languages are most commonly tested during technical rounds?

C++ is the most heavily tested language across Siemens core product groups (NX, Simcenter, EDA), followed closely by Java and Python. Web/cloud teams will focus on Java/Spring, Node.js, React, or C#/.NET, so tailor your preparation to the specific stack mentioned in the job description.

PracHub interview research ↗
Sources & methodology 3 sources ↗

No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.