De heffingsambtenaar herziet de belastingaanslag.

Because both nouns are definite here:

• de heffingsambtenaar = the tax official / assessment officer
• de belastingaanslag = the tax assessment

Dutch uses a definite article just like English uses the. In this sentence, both the person and the tax assessment are being referred to as specific, identifiable things.

Also, both heffingsambtenaar and belastingaanslag are de-words, so the article is de, not het.

Yes. Dutch very often forms long compound nouns by writing them as one word.

heffingsambtenaar is built from:

• heffing = levy, assessment, charging
• ambtenaar = civil servant, official

So together it means something like assessment official, tax official, or levying officer, depending on context.

This is very normal in Dutch. English often uses multiple words where Dutch prefers a single compound.

Because herziet is the conjugated verb form for he/she/it in the present tense.

The infinitive is herzien = to revise / to review / to reconsider.

Present tense:

• ik herzie
• jij herziet / herzie
• hij/zij/u herziet
• wij/jullie/zij herzien

In this sentence, the subject is de heffingsambtenaar, which is grammatically third person singular, so the verb must be herziet.

Herzien is an irregular verb. It is related to zien (to see), and that is why its forms may look a little unusual.

A few important forms are:

• infinitive: herzien
• present singular: herzie / herziet
• past: herzag
• past participle: herzien

In this sentence, you only need the present singular form: herziet.

No. Herzien is generally treated as an inseparable verb.

That means the prefix her- stays attached to the verb:

• De heffingsambtenaar herziet de belastingaanslag.

It does not split the way a separable verb would.

Compare:

• inseparable: herzien → hij herziet
• separable example: opbellen → hij belt ... op

So you should keep herziet together as one word.

Belastingaanslag is a specific tax term. It usually means a tax assessment or tax bill/notice of assessment, not just tax in general.

It is made up of:

• belasting = tax
• aanslag = assessment, levy, imposed charge

So this is not the same as:

• belasting = tax in general
• belastingaangifte = tax return
• belastingdienst = tax authority / tax service

This is a useful distinction, because English speakers often confuse tax return and tax assessment, but Dutch uses different words for them.

Because this is a simple main clause in standard Dutch word order:

• De heffingsambtenaar = subject
• herziet = finite verb
• de belastingaanslag = direct object

So the pattern is basically:

Subject + Verb + Object

That is very common in Dutch main clauses when nothing else comes first.

If another element came first, Dutch would still keep the finite verb in second position:

• Vandaag herziet de heffingsambtenaar de belastingaanslag.

That verb-second rule is one of the most important Dutch word-order rules.

Yes, grammatically that is fine, but it changes the meaning.

• De heffingsambtenaar herziet de belastingaanslag.
  = a specific official is revising a specific tax assessment

• Een heffingsambtenaar herziet een belastingaanslag.
  = a tax official is revising a tax assessment, in a more general or indefinite sense

So the difference is not grammar correctness, but definiteness.

It can mean any of those, depending on context.

For herzien, common English equivalents include:

• to revise
• to review
• to reconsider
• to reassess

In legal, tax, or administrative contexts, herzien often suggests that an earlier decision or document is being officially reviewed and possibly changed.

So in this sentence, revises or reviews are both plausible translations, depending on the context you were given.

A rough English-friendly guide:

• heffingsambtenaar ≈ HEF-fings-amp-tuh-NAHR
• herziet ≈ hair-ZEET
• belastingaanslag ≈ buh-LAS-ting-ahn-slahkh

A few useful notes:

• g in Dutch is usually a harsher throat sound than English g
• aa is a long vowel
• Dutch compounds are usually pronounced with the stress on one of the earlier main parts, though exact stress can vary a bit by region and speech style

If you want to sound natural, it helps to learn the pronunciation of the smaller parts:

• belasting
• aanslag
• ambtenaar

Yes, very much so. The vocabulary is administrative/legal.

Words like:

• heffingsambtenaar
• belastingaanslag
• herzien

belong to official, bureaucratic, or legal Dutch rather than everyday casual conversation.

A Dutch learner may not need to use this sentence often in speech, but it is exactly the kind of language you may see in:

• government letters
• tax documents
• legal decisions
• official notices

So it is useful mainly for reading formal Dutch.