Why MyBloodlines Only Records Parent-Child Ties

Open most family history tools and you’ll find yourself specifying all kinds of relationships by hand: this person is a sibling, that one’s a cousin, these two are spouses, this one’s a step-parent. MyBloodlines asks you to record exactly one kind of relationship: parent and child. Everything else — siblings, grandparents, cousins, spouses, in-laws — is worked out automatically from that.

This isn’t a limitation. It’s the single decision that keeps the whole bloodline consistent.

The one fact that never changes

Think about which family facts are actually permanent. A marriage can end. A “family friend” can become a stepparent. Someone’s understanding of who counts as a cousin can shift depending on which side of the family they grew up close to. But a parent-child relationship — the biological fact of who someone’s parents are — doesn’t change based on circumstance, relationship status, or how close two people feel to each other.

That’s why it’s the one relationship MyBloodlines lets you record directly. It’s the one piece of family structure that’s genuinely immutable, and building the entire bloodline on immutable facts is what keeps it from ever contradicting itself.

Every other relationship you’d normally think of as “family” — sibling, grandparent, aunt, cousin, spouse — is a pattern that emerges from a combination of parent-child links, not a separate fact that needs to be entered and kept in sync. So MyBloodlines doesn’t ask you to enter them. It derives them.

A simple worked example

Say you record that Maria is the mother of both Elena and Tomás. You didn’t tell MyBloodlines that Elena and Tomás are siblings — but they now show up connected as siblings, because that’s simply what it means for two people to share a parent. Later, someone records that Elena is the mother of a daughter, Sofia. Nobody needs to separately note that Maria is Sofia’s grandmother, or that Sofia and Tomás are aunt/uncle and niece/nephew, or that Tomás is Sofia’s uncle. All of that falls directly out of the two parent-child links that were actually recorded: Maria→Elena, Maria→Tomás, and Elena→Sofia.

Now suppose Tomás marries someone from a completely different bloodline. That marriage doesn’t get typed in as a standalone fact sitting off to the side — it becomes real the moment the couple’s shared child is recorded, connecting Tomás’s side and his spouse’s side through that child’s two parent-child links. The spousal relationship is simply what’s implied when two people share a parent-child connection to the same child. There’s more on exactly how that cross-bloodline connection gets made — since it involves two previously separate bloodlines — in how to add a child when parents are from different bloodlines.

Why deriving everything else matters

If MyBloodlines let you type in “sibling,” “cousin,” or “spouse” directly, as separate facts, you’d eventually end up with contradictions. Someone might record two people as siblings, while the actual parent-child links on file don’t support that — maybe one of them has a different mother nobody thought to correct. Now the bloodline is holding two different, conflicting versions of the truth, and there’s no way to tell which one is right without digging back through every entry that touches those people.

By deriving every relationship other than parent-child, that category of error simply can’t happen. Siblings are whoever shares a recorded parent — full stop, no separate entry to drift out of sync. Cousins are whoever shares a recorded grandparent. A grandparent is whoever is a parent of a parent. None of these can contradict the underlying parent-child facts, because they aren’t independent facts at all — they’re just labels applied to the shape those facts already make.

This is also what makes the bloodline resistant to duplication. Because every relationship is calculated fresh from the same underlying parent-child links, there’s no separate “sibling list” or “spouse list” sitting somewhere that could get out of date. Change or add a parent-child link, and everything that depends on it — down to distant cousins several links away — updates automatically and correctly.

Why this scales without getting harder to maintain

The further a bloodline grows, the more this rule matters. A small family with a handful of recorded people is easy enough to keep straight no matter how relationships are entered. But as more generations, more branches, and more distant relatives accumulate, manually maintained relationship labels become steadily harder to keep consistent — every new person is another chance for someone to mislabel a connection or forget to update a sibling list somewhere. Because MyBloodlines only ever asks for the one immutable fact and derives the rest, the bloodline doesn’t get more fragile as it grows. A cousin connection three generations removed is exactly as reliable as a direct sibling link, because both are computed the same way, from the same kind of underlying fact, with no additional manual bookkeeping required as the structure expands.

What this means for you, in practice

Recording a person into MyBloodlines mostly comes down to one question: who are this person’s parents, and/or who are their children? Once those links exist, the rest of that person’s place in the bloodline — their siblings, their aunts and uncles, their cousins, eventually their own spouse and children — takes care of itself as more of the bloodline gets filled in around them.

This is also why MyBloodlines can support one single, shared graph rather than a separate private tree per user. Because relationships are derived from immutable, unambiguous parent-child facts rather than entered by hand from each person’s own perspective, there’s no risk of your version of “how we’re related” quietly diverging from a cousin’s version. There’s exactly one structure, and it’s the same for everyone connected to it. How that shared, ownerless structure actually gets built and maintained by multiple relatives is covered in one shared family history: how relatives record together. And for how this data-model choice fits into the wider landscape of family history software, see the best family history & genealogy apps compared.

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