Ο όγκος δεδομένων είναι μεγάλος.

Ο is the masculine singular nominative definite article, meaning the.

It appears because όγκος is a masculine singular noun:

• ο όγκος = the volume / the bulk

So ο agrees with όγκος in gender, number, and case.

In this sentence, όγκος means volume, bulk, or amount in a fairly formal or technical sense.

So όγκος δεδομένων is a common way to say:

• volume of data
• data volume
• sometimes amount of data

It is especially natural in technical, scientific, or business contexts.

Because after όγκος, Greek uses the genitive to mean of data.

So the structure is:

• ο όγκος δεδομένων
• literally: the volume of data

Here:

• δεδομένα = nominative/accusative plural, data
• δεδομένων = genitive plural, of data

This is a very common Greek pattern:

• ο αριθμός φοιτητών = the number of students
• η ποσότητα νερού = the quantity of water
• ο όγκος δεδομένων = the volume of data

The dictionary form is usually δεδομένο in the singular, or δεδομένα when referring to data.

In modern Greek:

• το δεδομένο = a datum / a given fact / a data point, depending on context
• τα δεδομένα = data

In your sentence, the word appears in the genitive plural:

• δεδομένων = of data

Greek often leaves out the article in this kind of noun + genitive expression when it is being used in a general or category-like way.

So:

• ο όγκος δεδομένων = the volume of data in a general sense

You can also say:

• ο όγκος των δεδομένων

That usually sounds more specific, like:

• the volume of the data
• referring to some particular data already mentioned

So both are possible, but the version without των is very natural in general or technical statements.

Because the grammatical subject of the sentence is ο όγκος, not δεδομένων.

The sentence is built like this:

• Ο όγκος δεδομένων = the volume of data
• είναι μεγάλος = is large

So the verb agrees with όγκος, which is singular:

• ο όγκος ... είναι

Even though δεδομένων refers to many data items, it is not the subject here. It is just part of the phrase όγκος δεδομένων.

Because μεγάλος agrees with όγκος, the subject.

Agreement in Greek applies to:

• gender
• number
• case

Since όγκος is:

• masculine
• singular
• nominative

the adjective must also be:

• masculine
• singular
• nominative

So:

• ο όγκος ... είναι μεγάλος

Not:

• μεγάλα, because that would agree with a neuter plural noun such as δεδομένα
• μεγάλη, because that would be feminine singular

Because your sentence is using μεγάλος as a predicate adjective after είναι.

There are two different patterns:

1. Attributive adjective inside the noun phrase

   • ο μεγάλος όγκος δεδομένων
   • the large volume of data

2. Predicate adjective after είναι

   • ο όγκος δεδομένων είναι μεγάλος
   • the volume of data is large

Both are correct, but they do different jobs.

Yes, but it is a bit more formal and technical.

Ο όγκος δεδομένων είναι μεγάλος sounds like:

• The volume of data is large
• The amount of data is large

If you want a more everyday way to say there is a lot of data, Greek speakers might also say:

• Υπάρχουν πολλά δεδομένα = There is a lot of data / There are many data items
• Έχουμε πολλά δεδομένα = We have a lot of data

So your sentence is very natural when you want to emphasize volume or speak in a more formal register.

Yes. Greek word order is more flexible than English.

The neutral word order here is:

• Ο όγκος δεδομένων είναι μεγάλος.

But other orders are possible for emphasis, for example:

• Μεγάλος είναι ο όγκος δεδομένων.
• Είναι μεγάλος ο όγκος δεδομένων.

These alternatives can sound more emphatic or stylistically marked. For learners, the original order is the safest and most neutral.

A good approximate pronunciation is:

• O ONG-kos the-tho-ME-non EE-ne ME-gha-los

More carefully:

• Ο = o
• όγκος = stress on the first syllable
• δεδομένων = stress on μέ
• είναι = usually pronounced roughly EE-ne
• μεγάλος = stress on γά

A few sound notes:

• δ sounds like th in this
• γ before α, ο, ου is a voiced throat sound, not an English hard g
• the stress marks in Greek show which syllable is emphasized

It is in the nominative singular.

That is because it is the subject of the sentence:

• Ο όγκος δεδομένων = the volume of data

The nominative is the usual case for the subject in Greek.

So the core grammar is:

• όγκος = nominative singular subject
• δεδομένων = genitive plural dependent noun
• μεγάλος = nominative singular adjective agreeing with όγκος

Yes. That is a very good translation in a technical context.

Depending on context, possible English translations include:

• The volume of data is large.
• The data volume is large.
• The amount of data is large.

The exact best choice depends on style:

• volume of data sounds slightly more literal
• data volume sounds more technical
• amount of data sounds more general and natural in everyday English