About Constantia of Vienne
From the Foundation for Medieval Genealogy page on Provence:
Boson II married CONSTANTIA, daughter of --- (-after May ).
"Boso comes et uxor sua Constantia…illorum filii…Willelmus comes, Rotbaldus comes, Pontius juvenis" signed the charter dated May  under which "Gencius et uxor mea Aiburga" donated property "in pago Aquense superiore ad castrum…Ansoyse" to Monmajour.
Her affiliation is unknown. Chaume proposed that she was Constantia, daughter of Charles Constantin Comte de Vienne, for onomastic reasons only on the basis that names with the root "Constant-" were unknown in western royal genealogy before Charles Constantin himself. This supposition is, however, incorrect as numerous charters of the monastery of Cluny dated between 891 and 946 include the name "Constantia", and many others during the same period the names "Constantius" and "Constantinus". Poly suggests that Constantia, wife of Count Boson II, was the sister rather than daughter of Charles Constantin, but this appears to be more difficult to sustain chronologically.
Boson & his wife had two children:
1. Guillaume II (b. 955, d. 993 after 29 August in Avignon, Comte de Provence)
2. Rotbald II (d. 1008/22 April 1015, Comte de Provence)
From the Francogene website:
The family of Boso de PROVENCE and Constance de PROVENCE
 PROVENCE (de), Boso (Rotbold & Ermengarde d'AQUITAINE )
- married about 945, from France ? (France)
PROVENCE (de), Constance (Charles-Constantin & .. ), born about 925
1) Guillaume II, comte de Provence et d'Arles, born about 950, married about 980 Adèle dite Blanche d'ANJOU
Bibliographie : Essai sur l'histoire des comtes souverains de Provence; Histoire de la maison royale de France (Père Anselme)
From the French Wikipedia page for Constance de Provence:
Constance, née aux alentours de l'an 920, morte entre 963 et 966 fut comtesse de Provence par mariage.
Une filation mal connue
Sa filiation n'est pas connue et l'abbé Maurice Chaume a le premier mis en évidence que le prénom de cette dernière renvoyait au comte de Vienne Charles-Constantin. Il cite d'autres indices qui ne se révélèrent pas probants par la suite, mais considérer Charles Constantin, comte de Vienne comme le père de Constance de Provence reste la meilleure hypothèse de la filiation de Constance.
Certains chercheurs ont pensé qu'elle était sœur de Charles Constantin, mais Guillaume le Libérateur, son fils, étant né vers 950-955, elle même n'a pas pu naître avant 910-915. Or la mère de Charles Constantin, qui a transmis les prénoms de Constance et Constantin, est morte en 903. Il est vrai que Constance pourrait être une nièce de Charles Constantin, mais il est très improbable que ce dernier aie eu une sœur ou un frère germain (brièveté du mariage des parents et absence dans les sources).
Mariage et enfants
Elle épousa avant 942, ou plus probablement vers 945-948, Boson II (928 † 968), comte d'Arles et eut deux fils :
1. Rotbald (Roubaud) († 1008) et
2. Guillaume dit le Libérateur (†993) , né vers 950 et mort après le 29 août 993, comte d'Arles et de Provence puis marquis de Provence en 975. Il est le père de Constance d'Arles épouse du roi de Robert II de France.
Christian Settipani, Nos ancêtres de l'Antiquité : étude des possibilités de liens généalogiques entre les familles de l'Antiquité et celles du haut Moyen-Âge européen, Christian, Paris, 1991, 263 p. (ISBN 2-86496-050-6)
Christian Settipani, La Préhistoire des Capétiens (Nouvelle histoire généalogique de l'auguste maison de France, vol. 1), éd. Patrick van Kerrebrouck, 1993 (ISBN 2-9501509-3-4)
1.↑ Constantia is named as the wife of Comte Boson, and mother of Guillaume and Rotbald, in the Cartulaire de Montmajour dated May 963 (Chartrier de Saint-Pierre de Montmajour, ed. Dom Chantelou (1890/1), pp. 1-384, quoted in Settipani (1991), p. 3 footnote 3.)
Constance was born around 920 and died between 963 and 966. She was Comtesse de Provence by marriage.
A little known woman
Her parentage is unknown, though Father Maurice Chaume suggested that her name came from the Comte de Vienne, Charles Constantine. He cites other evidence that proved to be inconclusive afterward, but considering Charles Constantine, Comte de Vienne, as the father of Constance de Provence is the best hypothesis so far of Constance's ancestry.
Some researchers have thought she was the sister of Charles Constantine, but his son, William the Deliverer, was born around 950-955, and Charles himself was not born before 910-915. Now the mother of Charles Constantine, who carried forward the names of Constance and Constantine, died in 903. It is true that Constance could be a niece of Charles Constantine, but it is unlikely that the latter was a sister or brother (short of an omission of parentage or marriage in the sources).
Marriage and Children
She married before 942, or more likely 945-948, to Boson II (928-968), Comte d'Arles. They had two sons :
1. Rotbald (Robaud) (d. 1008)
2. William The Liberator (d. 993), born c. 950 and died after 29 August 993, Comte d'Arles and Provence, and Marquis de Provence in 975. He is the father of Constance of Arles, who became wife of King Robert II of France.
1. Constantia is named as the wife of Count Boson, and mother of Guillaume and Rotbald, in the Cartulary Montmajour dated May 963 (Charter of St-Pierre-Montmajour, ed. Chantelou Dom 1890/1, pp 1-384, quoted in Settipani 1991, p. 3, footnote 3.)
Constance OF VIENNE7,207 was born about 935. ARSC 6TH ED LINE 141A,B PED OF A.H.AYERS Parents: \Count Of Vienne\ Charles CONSTANTINE and TEUTBERGE.
Spouse: Count Of Provence & Arles BOSO. Count Of Provence & Arles BOSO and Constance OF VIENNE were married. Children were: Count Of Provenc\ Rotbaud II, Count Of Provenc\ William I.
William I of Provence
From Wikipedia, the free encyclopedia
He and his elder brother Rotbold II, sons of Boso II of Arles and Constance of Viennois, daughter of Charles-Constantine. -------------------- From Wikipedia, the free encyclopedia William I (c. 950 – after 29 August 993), called the Liberator, was Count of Provence from 968 to his abdication. In 975 or 979, he took the title of marchio or margrave. He is often considered the founder of the county of Provence. He and his elder brother Rotbold II were sons of Boso II of Arles and Constance of Viennois, daughter of Charles-Constantine. They both carried the title of comes or count concurrently, but it is unknown if they were joint-counts of the whole of Provence or if the region was divided. His brother never bore any other title than count so long as William lived, so the latter seems to have attained a certain supremacy.
William I, Count of Provence, and Adelaide of Anjou. William was the son of Boso II, Count of Arles, and Constance of Viennois. Adelaide was the daughter of Fulk II the the Good of Anjou and Gerberga.
Charles Constantine of Vienne
Charles-Constantine (died 962) was the Count of Vienne, son of Louis the Blind, King of Provence, and the Holy Roman Emperor.
Name and maternity
About his name; he was never called "Charles Constantine", rather Flodoard, copied later by Richar, calls him "Constantinus". We know that his proper name was "Carolus" (Charles), from a diploma of his father, and from his own charters. Modern scholars have typically called him Charles Constantine, but this was not a name used during his lifetime.
Some modern genealogical scholars speculated that his mother was Anna of Constantinople, daughter of Leo VI the Wise and his second wife Zoe Zaoutzaina. However, his father's marriage to this princess is much disputed and rather unlikely. Christian Settipani postulates that his name refers to the founders of the empires governed by his father and maternal grandfather, i.e., to Charlemagne and Constantine the Great.
Regarding his birthyear, or age, we have few datapoints. He was Count of Vienne and acting as an adult by (but not in) December 927. This evidences that his father must have had a prior union. Some speculation would place him born in 901/3 but this is just a force-fit to allow Anna to be his mother and his father's wife.
When Charles' father Louis died in 929, Hugh of Arles, who was already king of Italy, took over Provence and gave it, in 933, to King Rudolf II of Burgundy. Charles-Constantine for whatever reason, could not inherit his father's right to the imperial throne or his right to rule Provence. This has led many to believe he was, in fact, a bastard. He did however rule the county of the Viennois, until his death in 962.
He was married to Thiberge de Troyes.
It has been speculated that Constance, wife to Boso II of Arles and grandmother of Queen Constance of Arles, was their daughter .Through her, Charles Constantine would be an ancestor of the Capetian kings of France and the Norman and Plantagenet kings of England (through Queen Constance's daughter Adela Capet, and Adela's daughter Queen Matilda of Flanders, who married William the Conqueror).
Constantia of Vienne's Timeline
Carpentras, Comtat Venaissin, Provence, France