Buku harian saya ada di atas meja.

In Indonesian, possession is usually shown by putting the possessor after the thing possessed.

So:

• buku harian = diary
• saya = I / me / my

Putting them together:

• buku harian saya = my diary

This is different from English, where my comes before the noun.

A similar pattern:

• rumah saya = my house
• teman saya = my friend

Buku harian is the normal Indonesian expression for diary.

Literally, it is made of:

• buku = book
• harian = daily / related to days

So the literal sense is something like daily book, but in natural English that becomes diary or sometimes journal.

This is a fixed, common expression. Native speakers understand buku harian as a diary, not just any book.

Here, ada shows existence or location. In this sentence, it means something like is there or is located.

So:

• Buku harian saya ada di atas meja = My diary is on the table

Indonesian often uses ada when saying where something is.

Compare:

• Buku itu ada di tas saya = The book is in my bag
• Ibu ada di rumah = Mom is at home

So ada is not exactly the same as English is, but in location sentences it often fills that role.

Because adalah is generally used to connect a subject with a noun phrase in definitions or formal statements, not for location.

For example:

• Dia adalah guru = He/She is a teacher

But for location, Indonesian normally uses ada or sometimes berada:

• Dia ada di rumah = He/She is at home
• Dia berada di rumah = He/She is at home (more formal)

So:

• Buku harian saya ada di atas meja = correct
• Buku harian saya adalah di atas meja = unnatural / incorrect

Di atas means on, on top of, or above, depending on context.

It is made of:

• di = a preposition meaning in / at / on
• atas = top / upper part

Together:

• di atas meja = on the table / above the table

It is written as two words because di here is a preposition.

This is important in Indonesian:

• di atas = on top of
• di rumah = at home
• di sekolah = at school

But di- written attached to a word is usually a verb prefix:

• ditulis = written
• dibaca = read

So in your sentence, di atas must be written separately.

It can mean either, depending on context, but very often it means on the table.

In everyday Indonesian, di atas meja is commonly used for something resting on the surface of the table.

If needed, context makes it clear:

• If the diary is physically lying there, di atas meja naturally means on the table
• If it is hovering or positioned higher than the table, it could mean above the table

So this phrase is broader than English on, but in many normal situations on the table is the best translation.

Indonesian does not usually use articles like a, an, or the the way English does.

So:

• meja can mean a table, the table, or just table, depending on context

In your sentence, English naturally uses the table, but Indonesian does not need a separate word for that.

This is very common:

• Saya beli buku = I bought a book / the book
• Kucing ada di kursi = The cat is on the chair / a cat is on a chair

The exact meaning depends on the situation.

Sometimes yes, especially in casual speech, but ada is very natural and standard when talking about location.

So you may hear:

• Buku harian saya di atas meja

This can still be understood as My diary is on the table, especially in conversation.

However, the fuller version:

• Buku harian saya ada di atas meja

sounds clearer and more complete, especially for learners and in neutral standard Indonesian.

You might also see:

• Buku harian saya berada di atas meja

This is more formal than ada.

You could also use aku, depending on the situation.

Compare:

• buku harian saya = my diary
• buku harian aku = my diary

The difference is mainly tone:

• saya = neutral, polite, standard
• aku = informal, personal, used with friends, family, or in casual writing

So the original sentence sounds neutral and safe in most contexts.

Indonesian works differently from English. It often does not need a direct equivalent of am / is / are in many sentences.

For example:

• Dia guru = He/She is a teacher
• Saya lelah = I am tired

In location sentences, though, Indonesian often uses ada:

• Dia ada di kantor = He/She is at the office

So the language does not rely on one all-purpose verb like English to be. Instead, different sentence types are handled in different ways.

Yes, it is natural and correct.

It sounds like normal everyday Indonesian and would be easily understood by native speakers. It is a good example of a basic location sentence:

• [thing] + ada + [place]

For example:

• Tas saya ada di kamar = My bag is in the room
• Kunci mobil ada di meja = The car keys are on the table

So your sentence follows a very common and useful pattern.