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#1
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Confused about one-to-many or many-to-many relationships
Hello,
I am in the process of designing the tables for a parcel acquisition and lease database. I will have two tables, tblPropertyInfo (tPI) and tblOwnerInfo (tOI). The tPI will have the Tax Assessment ID (TAID)as the PK. The tOI will have the SSN of the owner as the PK. Here are some relationships that exist in each table. Table structures -the tOI will also have name, phone, and address fields, with the tPI's TAID as the FK*, and have the FK indexed and to accept duplicates. - the tPI will also have township, range, section, tract fields, with the fOI's SSN as the FK*,and have the FK indexed and to accept duplicates. * NOTE: I'm assuming that this is a proper, necessary implementation, putting the aforementioned FK's as shown in their respective table structures, right? Here are some scenarios: A) John and Sally Smith own parcel A B) John Smith also owns parcel B, and C C) Sally Smith owns 50% of parcel D D) Joe Johnson (Sally's brother) owns the other 50% of parcel D Relationships 1 - Scenario A is a Many-to-One relationship (MTO) 2 - Scenario B is a One-to-Many relationship (OTM) 3 - Scenario C is a One-to-One relationship (OTO) 4 - Scenario D is a One-to-One relationship (OTO) Here are my questions: 1 - Are my relationships correct? Or are there any Many-to-Many relationships shown? 2- In the process of doing the relationship diagram, when I choose the PK from the tOI (SSN) and drag it to the tPI FK (SSN), which of those 3 options (see ** below) should I choose? 3 - When I constructing the form and say I'm making the field SSN, for example. How can I enable it so that I don't have to enter the SSN twice in the two tables? Theoretically, I should only have to enter it into the tOI. But I'm missing something here, I think --------------------------------------- ** Edit Relationships Dialog/Join Type Button/Join Properties: 1) Only include rows where... 2) Include ALL records from 'tblOwnerInfo' and only those from the 'tblPropertyInfo' where the joined fields are equal. 3) Include ALL records from 'tblPropertyInfo' and only those from the 'tblOwnerInfo' where the joined fields are equal. --------------------------------------- As a side note, can anyone recommend a good site that explains Join Properties well, to a beginner like myself? I know that these are VERY fundamental issues for 90% of those of you who read these posts, but I REALLY need to get a grip on this before I move on to create the rest of the database for this project. TIA. Phil. |
#2
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On Wed, 06 Jul 2005 11:48:38 -0700, CAD Fiend
wrote: Hello, I am in the process of designing the tables for a parcel acquisition and lease database. I will have two tables, tblPropertyInfo (tPI) and tblOwnerInfo (tOI). The tPI will have the Tax Assessment ID (TAID)as the PK. The tOI will have the SSN of the owner as the PK. Here are some relationships that exist in each table. Table structures -the tOI will also have name, phone, and address fields, with the tPI's TAID as the FK*, and have the FK indexed and to accept duplicates. - the tPI will also have township, range, section, tract fields, with the fOI's SSN as the FK*,and have the FK indexed and to accept duplicates. * NOTE: I'm assuming that this is a proper, necessary implementation, putting the aforementioned FK's as shown in their respective table structures, right? No. It is not correct. There should be NOTHING concerning the property in tOI, and NOTHING concerning the owner in tPI. Here are some scenarios: A) John and Sally Smith own parcel A B) John Smith also owns parcel B, and C C) Sally Smith owns 50% of parcel D D) Joe Johnson (Sally's brother) owns the other 50% of parcel D Relationships 1 - Scenario A is a Many-to-One relationship (MTO) 2 - Scenario B is a One-to-Many relationship (OTM) 3 - Scenario C is a One-to-One relationship (OTO) 4 - Scenario D is a One-to-One relationship (OTO) Well... yes. But these are relationships between *individual entities*. What you need for Access is the relationship between *TABLES*, or (in the real world) between classes of Entities, rather than individual instances of those entities. Here are my questions: 1 - Are my relationships correct? Or are there any Many-to-Many relationships shown? There is one Many to Many relationship. That's all. A given Property can be owned by zero, one, or many Owners. A given Owner can own zero, one, or many Properties. Property -- many-many -- Owner 2- In the process of doing the relationship diagram, when I choose the PK from the tOI (SSN) and drag it to the tPI FK (SSN), which of those 3 options (see ** below) should I choose? None of them, because you don't have a SSN in tPI, and you don't have a property ID in tOI. 3 - When I constructing the form and say I'm making the field SSN, for example. How can I enable it so that I don't have to enter the SSN twice in the two tables? Theoretically, I should only have to enter it into the tOI. But I'm missing something here, I think You need a THIRD TABLE - Ownership: tOwnership SSN FK to tOI, who owns the property TAID FK to tPI, what property do they own other fields, e.g. percentage ownership defaulting to 1.0 You would drag SSN from tOP to SSN in tOwnership; the three types of relationship are *almost* irrelevant, since they don't affect relational integrity. All they do is give you a default join type on a new query. In this case use option 1 - you are not interested in outer joins at this point, all you need to know is who owns what! Similarly, you'ld drag TAID from tPI to TAID in tOwnership. In your scenarios above, tOwnership would have records with (using names in place of ID's) John Smith Parcel A 1.0 community property? Sally Smith Parcel A 1.0 community property? John Smith Parcel B 1.0 John Smith Parcel C 1.0 Sally Smith Parcel D 0.5 Joe Johnson Parcel D 0.5 John W. Vinson[MVP] |
#3
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Thank you John, for taking the time to explain this properly to me. I
apprieciate your and everyone's patience when it comes to explaining (probably for the umteenth time) concepts that are probably old hat to you all, but new to newbies like myself. Phil. John Vinson wrote: On Wed, 06 Jul 2005 11:48:38 -0700, CAD Fiend wrote: Hello, I am in the process of designing the tables for a parcel acquisition and lease database. I will have two tables, tblPropertyInfo (tPI) and tblOwnerInfo (tOI). The tPI will have the Tax Assessment ID (TAID)as the PK. The tOI will have the SSN of the owner as the PK. Here are some relationships that exist in each table. Table structures -the tOI will also have name, phone, and address fields, with the tPI's TAID as the FK*, and have the FK indexed and to accept duplicates. - the tPI will also have township, range, section, tract fields, with the fOI's SSN as the FK*,and have the FK indexed and to accept duplicates. * NOTE: I'm assuming that this is a proper, necessary implementation, putting the aforementioned FK's as shown in their respective table structures, right? No. It is not correct. There should be NOTHING concerning the property in tOI, and NOTHING concerning the owner in tPI. Here are some scenarios: A) John and Sally Smith own parcel A B) John Smith also owns parcel B, and C C) Sally Smith owns 50% of parcel D D) Joe Johnson (Sally's brother) owns the other 50% of parcel D Relationships 1 - Scenario A is a Many-to-One relationship (MTO) 2 - Scenario B is a One-to-Many relationship (OTM) 3 - Scenario C is a One-to-One relationship (OTO) 4 - Scenario D is a One-to-One relationship (OTO) Well... yes. But these are relationships between *individual entities*. What you need for Access is the relationship between *TABLES*, or (in the real world) between classes of Entities, rather than individual instances of those entities. Here are my questions: 1 - Are my relationships correct? Or are there any Many-to-Many relationships shown? There is one Many to Many relationship. That's all. A given Property can be owned by zero, one, or many Owners. A given Owner can own zero, one, or many Properties. Property -- many-many -- Owner 2- In the process of doing the relationship diagram, when I choose the PK from the tOI (SSN) and drag it to the tPI FK (SSN), which of those 3 options (see ** below) should I choose? None of them, because you don't have a SSN in tPI, and you don't have a property ID in tOI. 3 - When I constructing the form and say I'm making the field SSN, for example. How can I enable it so that I don't have to enter the SSN twice in the two tables? Theoretically, I should only have to enter it into the tOI. But I'm missing something here, I think You need a THIRD TABLE - Ownership: tOwnership SSN FK to tOI, who owns the property TAID FK to tPI, what property do they own other fields, e.g. percentage ownership defaulting to 1.0 You would drag SSN from tOP to SSN in tOwnership; the three types of relationship are *almost* irrelevant, since they don't affect relational integrity. All they do is give you a default join type on a new query. In this case use option 1 - you are not interested in outer joins at this point, all you need to know is who owns what! Similarly, you'ld drag TAID from tPI to TAID in tOwnership. In your scenarios above, tOwnership would have records with (using names in place of ID's) John Smith Parcel A 1.0 community property? Sally Smith Parcel A 1.0 community property? John Smith Parcel B 1.0 John Smith Parcel C 1.0 Sally Smith Parcel D 0.5 Joe Johnson Parcel D 0.5 John W. Vinson[MVP] |
#4
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Phil,
In addition to John's great explanation, you might find this helpful... http://accesstips.datamanagementsolutions.biz/many.mht -- Steve Schapel, Microsoft Access MVP CAD Fiend wrote: Hello, I am in the process of designing the tables for a parcel acquisition and lease database. I will have two tables, tblPropertyInfo (tPI) and tblOwnerInfo (tOI). The tPI will have the Tax Assessment ID (TAID)as the PK. The tOI will have the SSN of the owner as the PK. Here are some relationships that exist in each table. Table structures -the tOI will also have name, phone, and address fields, with the tPI's TAID as the FK*, and have the FK indexed and to accept duplicates. - the tPI will also have township, range, section, tract fields, with the fOI's SSN as the FK*,and have the FK indexed and to accept duplicates. * NOTE: I'm assuming that this is a proper, necessary implementation, putting the aforementioned FK's as shown in their respective table structures, right? Here are some scenarios: A) John and Sally Smith own parcel A B) John Smith also owns parcel B, and C C) Sally Smith owns 50% of parcel D D) Joe Johnson (Sally's brother) owns the other 50% of parcel D Relationships 1 - Scenario A is a Many-to-One relationship (MTO) 2 - Scenario B is a One-to-Many relationship (OTM) 3 - Scenario C is a One-to-One relationship (OTO) 4 - Scenario D is a One-to-One relationship (OTO) Here are my questions: 1 - Are my relationships correct? Or are there any Many-to-Many relationships shown? 2- In the process of doing the relationship diagram, when I choose the PK from the tOI (SSN) and drag it to the tPI FK (SSN), which of those 3 options (see ** below) should I choose? 3 - When I constructing the form and say I'm making the field SSN, for example. How can I enable it so that I don't have to enter the SSN twice in the two tables? Theoretically, I should only have to enter it into the tOI. But I'm missing something here, I think --------------------------------------- ** Edit Relationships Dialog/Join Type Button/Join Properties: 1) Only include rows where... 2) Include ALL records from 'tblOwnerInfo' and only those from the 'tblPropertyInfo' where the joined fields are equal. 3) Include ALL records from 'tblPropertyInfo' and only those from the 'tblOwnerInfo' where the joined fields are equal. --------------------------------------- As a side note, can anyone recommend a good site that explains Join Properties well, to a beginner like myself? I know that these are VERY fundamental issues for 90% of those of you who read these posts, but I REALLY need to get a grip on this before I move on to create the rest of the database for this project. TIA. Phil. |
#5
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Thanks Steve, I will check it out.
Steve Schapel wrote: Phil, In addition to John's great explanation, you might find this helpful... http://accesstips.datamanagementsolutions.biz/many.mht -- Steve Schapel, Microsoft Access MVP CAD Fiend wrote: Hello, I am in the process of designing the tables for a parcel acquisition and lease database. I will have two tables, tblPropertyInfo (tPI) and tblOwnerInfo (tOI). The tPI will have the Tax Assessment ID (TAID)as the PK. The tOI will have the SSN of the owner as the PK. Here are some relationships that exist in each table. Table structures -the tOI will also have name, phone, and address fields, with the tPI's TAID as the FK*, and have the FK indexed and to accept duplicates. - the tPI will also have township, range, section, tract fields, with the fOI's SSN as the FK*,and have the FK indexed and to accept duplicates. * NOTE: I'm assuming that this is a proper, necessary implementation, putting the aforementioned FK's as shown in their respective table structures, right? Here are some scenarios: A) John and Sally Smith own parcel A B) John Smith also owns parcel B, and C C) Sally Smith owns 50% of parcel D D) Joe Johnson (Sally's brother) owns the other 50% of parcel D Relationships 1 - Scenario A is a Many-to-One relationship (MTO) 2 - Scenario B is a One-to-Many relationship (OTM) 3 - Scenario C is a One-to-One relationship (OTO) 4 - Scenario D is a One-to-One relationship (OTO) Here are my questions: 1 - Are my relationships correct? Or are there any Many-to-Many relationships shown? 2- In the process of doing the relationship diagram, when I choose the PK from the tOI (SSN) and drag it to the tPI FK (SSN), which of those 3 options (see ** below) should I choose? 3 - When I constructing the form and say I'm making the field SSN, for example. How can I enable it so that I don't have to enter the SSN twice in the two tables? Theoretically, I should only have to enter it into the tOI. But I'm missing something here, I think --------------------------------------- ** Edit Relationships Dialog/Join Type Button/Join Properties: 1) Only include rows where... 2) Include ALL records from 'tblOwnerInfo' and only those from the 'tblPropertyInfo' where the joined fields are equal. 3) Include ALL records from 'tblPropertyInfo' and only those from the 'tblOwnerInfo' where the joined fields are equal. --------------------------------------- As a side note, can anyone recommend a good site that explains Join Properties well, to a beginner like myself? I know that these are VERY fundamental issues for 90% of those of you who read these posts, but I REALLY need to get a grip on this before I move on to create the rest of the database for this project. TIA. Phil. |
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